(window.webpackJsonp=window.webpackJsonp||[]).push([[629],{1039:function(t,s,a){"use strict";a.r(s);var n=a(31),e=Object(n.a)({},(function(){var t=this,s=t.$createElement,a=t._self._c||s;return a("ContentSlotsDistributor",{attrs:{"slot-key":t.$parent.slotKey}},[a("h1",{attrs:{id:"classes-structures"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#classes-structures"}},[t._v("#")]),t._v(" Classes/Structures")]),t._v(" "),a("h2",{attrs:{id:"class-basics"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#class-basics"}},[t._v("#")]),t._v(" Class basics")]),t._v(" "),a("p",[t._v("A "),a("strong",[t._v("class")]),t._v(" is a user-defined type. A class is introduced with the "),a("code",[t._v("class")]),t._v(", "),a("code",[t._v("struct")]),t._v(" or "),a("code",[t._v("union")]),t._v(' keyword. In colloquial usage, the term "class" usually refers only to non-union classes.')]),t._v(" "),a("p",[t._v("A class is a collection of "),a("strong",[t._v("class members")]),t._v(", which can be:")]),t._v(" "),a("ul",[a("li",[t._v('member variables (also called "fields"),')]),t._v(" "),a("li",[t._v('member functions (also called "methods"),')]),t._v(" "),a("li",[t._v('member types or typedefs (e.g. "nested classes"),')]),t._v(" "),a("li",[t._v("member templates (of any kind: variable, function, class or alias template)")])]),t._v(" "),a("p",[t._v("The "),a("code",[t._v("class")]),t._v(" and "),a("code",[t._v("struct")]),t._v(" keywords, called "),a("strong",[t._v("class keys")]),t._v(', are largely interchangeable, except that the default access specifier for members and bases is "private" for a class declared with the '),a("code",[t._v("class")]),t._v(' key and "public" for a class declared with the '),a("code",[t._v("struct")]),t._v(" or "),a("code",[t._v("union")]),t._v(" key (cf. "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/c%2b%2b/508/classes-structures/1668/access-modifiers",target:"_blank",rel:"noopener noreferrer"}},[t._v("Access modifiers"),a("OutboundLink")],1),t._v(").")]),t._v(" "),a("p",[t._v("For example, the following code snippets are identical:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Vector")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" y"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" z"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// are equivalent to")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Vector")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" y"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" z"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("By declaring a class` a new type is added to your program, and it is possible to instantiate objects of that class by")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[t._v("Vector my_vector"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Members of a class are accessed using dot-syntax.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[t._v("my_vector"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nmy_vector"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("y "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" my_vector"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// my_vector.y = 11;")]),t._v("\nmy_vector"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("z "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" my_vector"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("y "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("4")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// my:vector.z = 7;")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"final-classes-and-structs"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#final-classes-and-structs"}},[t._v("#")]),t._v(" Final classes and structs")]),t._v(" "),a("p",[t._v("Deriving a class may be forbidden with "),a("code",[t._v("final")]),t._v(" specifier. Let's declare a final class:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("final")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Now any attempt to subclass it will cause a compilation error:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Compilation error: cannot derive from final class:")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Final class may appear anywhere in class hierarchy:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// OK.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("final")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" A "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Compilation error: cannot derive from final class B.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("C")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"access-specifiers"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#access-specifiers"}},[t._v("#")]),t._v(" Access specifiers")]),t._v(" "),a("p",[t._v("There are three "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/c%2b%2b/4891/keywords",target:"_blank",rel:"noopener noreferrer"}},[t._v("keywords"),a("OutboundLink")],1),t._v(" that act as "),a("strong",[t._v("access specifiers")]),t._v(". These limit the access to class members  following the specifier, until another specifier changes the access level again:")]),t._v(" "),a("table",[a("thead",[a("tr",[a("th",[t._v("Keyword")]),t._v(" "),a("th",[t._v("Description")])])]),t._v(" "),a("tbody",[a("tr",[a("td",[a("code",[t._v("public")])]),t._v(" "),a("td",[t._v("Everyone has access")])]),t._v(" "),a("tr",[a("td",[a("code",[t._v("protected")])]),t._v(" "),a("td",[t._v("Only the class itself, derived classes and friends have access")])]),t._v(" "),a("tr",[a("td",[a("code",[t._v("private")])]),t._v(" "),a("td",[t._v("Only the class itself and friends have access")])])])]),t._v(" "),a("p",[t._v("When the type is defined using the "),a("code",[t._v("class")]),t._v(" keyword, the default access specifier is "),a("code",[t._v("private")]),t._v(", but if the type is defined using the "),a("code",[t._v("struct")]),t._v(" keyword, the default access specifier is "),a("code",[t._v("public")]),t._v(":")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("MyStruct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("MyClass")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nMyStruct s"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\ns"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("9")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// well formed, because x is public")]),t._v("\n\nMyClass c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nc"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("9")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ill-formed, because x is private")]),t._v("\n\n")])])]),a("p",[t._v("Access specifiers are mostly used to limit access to internal fields and methods, and force the programmer to use a specific interface, for example to force use of getters and setters instead of referencing a variable directly:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("MyClass")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/* Methods: */")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("x")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("noexcept")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" m_x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("setX")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("noexcept")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" m_x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("private")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/* Fields: */")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" m_x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Using "),a("code",[t._v("protected")]),t._v(" is useful for allowing certain functionality of the type to be only accessible to the derived classes, for example, in the following code, the method "),a("code",[t._v("calculateValue()")]),t._v(" is only accessible to classes deriving from the base class "),a("code",[t._v("Plus2Base")]),t._v(", such as "),a("code",[t._v("FortyTwo")]),t._v(":")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Plus2Base")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("value")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("noexcept")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("calculateValue")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("protected")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/* Methods: */")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("virtual")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("calculateValue")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("noexcept")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("FortyTwo")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Plus2Base")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("protected")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/* Methods: */")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("calculateValue")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("noexcept")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("final")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("override")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("40")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Note that the "),a("code",[t._v("friend")]),t._v(" keyword can be used to add access exceptions to functions or types for accessing protected and private members.")]),t._v(" "),a("p",[t._v("The "),a("code",[t._v("public")]),t._v(", "),a("code",[t._v("protected")]),t._v(", and "),a("code",[t._v("private")]),t._v(" keywords can also be used to grant or limit access to base class subobjects. See the "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/c%2b%2b/508/classes-structures/1669/inheritance",target:"_blank",rel:"noopener noreferrer"}},[t._v("Inheritance"),a("OutboundLink")],1),t._v(" example.")]),t._v(" "),a("h2",{attrs:{id:"inheritance"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#inheritance"}},[t._v("#")]),t._v(" Inheritance")]),t._v(" "),a("p",[t._v("Classes/structs can have inheritance relations.")]),t._v(" "),a("p",[t._v("If a class/struct "),a("code",[t._v("B")]),t._v(" inherits from a class/struct "),a("code",[t._v("A")]),t._v(", this means that "),a("code",[t._v("B")]),t._v(" has as a parent "),a("code",[t._v("A")]),t._v(". We say that "),a("code",[t._v("B")]),t._v(" is a derived class/struct from "),a("code",[t._v("A")]),t._v(", and "),a("code",[t._v("A")]),t._v(" is the base class/struct.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" p1"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("protected")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" p2"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("private")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" p3"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//Make B inherit publicly (default) from A")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")])]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("There are 3 forms of inheritance for a class/struct:")]),t._v(" "),a("ul",[a("li",[a("code",[t._v("public")])]),t._v(" "),a("li",[a("code",[t._v("private")])]),t._v(" "),a("li",[a("code",[t._v("protected")])])]),t._v(" "),a("p",[t._v("Note that the default inheritance is the same as the default visibility of members: "),a("code",[t._v("public")]),t._v(" if you use the "),a("code",[t._v("struct")]),t._v(" keyword, and "),a("code",[t._v("private")]),t._v(" for the "),a("code",[t._v("class")]),t._v(" keyword.")]),t._v(" "),a("p",[t._v("It's even possible to have a "),a("code",[t._v("class")]),t._v(" derive from a "),a("code",[t._v("struct")]),t._v(" (or vice versa). In this case, the default inheritance is controlled by the child, so a "),a("code",[t._v("struct")]),t._v(" that derives from a "),a("code",[t._v("class")]),t._v(" will default to public inheritance, and a "),a("code",[t._v("class")]),t._v(" that derives from a "),a("code",[t._v("struct")]),t._v(" will have private inheritance by default.")]),t._v(" "),a("p",[a("code",[t._v("public")]),t._v(" inheritance:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// or just `struct B : A`")])]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        p1 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//well formed, p1 is public in B")]),t._v("\n        p2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//well formed, p2 is protected in B")]),t._v("\n        p3 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//ill formed, p3 is private in A")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nB b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nb"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("p1 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//well formed, p1 is public")]),t._v("\nb"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("p2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//ill formed, p2 is protected")]),t._v("\nb"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("p3 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//ill formed, p3 is inaccessible")]),t._v("\n\n")])])]),a("p",[a("code",[t._v("private")]),t._v(" inheritance:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("private")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")])]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        p1 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//well formed, p1 is private in B")]),t._v("\n        p2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//well formed, p2 is private in B")]),t._v("\n        p3 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//ill formed, p3 is private in A")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nB b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nb"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("p1 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//ill formed, p1 is private")]),t._v("\nb"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("p2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//ill formed, p2 is private")]),t._v("\nb"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("p3 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//ill formed, p3 is inaccessible")]),t._v("\n\n")])])]),a("p",[a("code",[t._v("protected")]),t._v(" inheritance:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("protected")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")])]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        p1 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//well formed, p1 is protected in B")]),t._v("\n        p2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//well formed, p2 is protected in B")]),t._v("\n        p3 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//ill formed, p3 is private in A")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nB b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nb"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("p1 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//ill formed, p1 is protected")]),t._v("\nb"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("p2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//ill formed, p2 is protected")]),t._v("\nb"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("p3 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//ill formed, p3 is inaccessible")]),t._v("\n\n")])])]),a("p",[t._v("Note that although "),a("code",[t._v("protected")]),t._v(" inheritance is allowed, the actual use of it is rare. One instance of how "),a("code",[t._v("protected")]),t._v(' inheritance is used in application is in partial base class specialization (usually referred to as "controlled polymorphism").')]),t._v(" "),a("p",[t._v('When OOP was relatively new, (public) inheritance was frequently said to model an "IS-A" relationship. That is, public inheritance is correct only if an instance of the derived class '),a("strong",[t._v("is also an")]),t._v(" instance of the base class.")]),t._v(" "),a("p",[t._v("This was later refined into the "),a("a",{attrs:{href:"https://en.wikipedia.org/wiki/Liskov_substitution_principle",target:"_blank",rel:"noopener noreferrer"}},[t._v("Liskov Substitution Principle"),a("OutboundLink")],1),t._v(": public inheritance should only be used when/if an instance of the derived class can be substituted for an instance of the base class under any possible circumstance (and still make sense).")]),t._v(" "),a("p",[t._v('Private inheritance is typically said to embody a completely different relationship: "is implemented in terms of" (sometimes called a "HAS-A" relationship). For example, a '),a("code",[t._v("Stack")]),t._v(" class could inherit privately from a "),a("code",[t._v("Vector")]),t._v(" class. Private inheritance bears a much greater similarity to aggregation than to public inheritance.")]),t._v(" "),a("p",[t._v("Protected inheritance is almost never used, and there's no general agreement on what sort of relationship it embodies.")]),t._v(" "),a("h2",{attrs:{id:"friendship"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#friendship"}},[t._v("#")]),t._v(" Friendship")]),t._v(" "),a("p",[t._v("The "),a("code",[t._v("friend")]),t._v(" "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/c%2b%2b/4891/keyword",target:"_blank",rel:"noopener noreferrer"}},[t._v("keyword"),a("OutboundLink")],1),t._v(" is used to give other classes and functions access to private and protected members of the class, even through they are defined outside the class`s scope.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Animal")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("private")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("double")]),t._v(" weight"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("double")]),t._v(" height"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("friend")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("printWeight")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("Animal animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("friend")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("AnimalPrinter")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// A common use for a friend function is to overload the operator<< for streaming. ")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("friend")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("ostream"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("operator")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("ostream"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" os"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" Animal animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("printWeight")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("Animal animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("cout "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("weight "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"\\n"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("AnimalPrinter")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" Animal"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// Because of the `friend class AnimalPrinter;" declaration, we are')]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// allowed to access private members here.")]),t._v("\n        std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("cout "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("weight "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('", "')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("height "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("endl"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\nstd"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("ostream"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("operator")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("ostream"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" os"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" Animal animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    os "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Animal height: "')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("height "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"\\n"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" os"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    Animal animal "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("printWeight")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    AnimalPrinter aPrinter"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    aPrinter"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("print")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("cout "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" animal"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token number"}},[t._v("10")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("10")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),t._v("\nAnimal height"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"virtual-inheritance"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#virtual-inheritance"}},[t._v("#")]),t._v(" Virtual Inheritance")]),t._v(" "),a("p",[t._v("When using inheritance, you can specify the "),a("code",[t._v("virtual")]),t._v(" keyword:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("virtual")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")])]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("When class "),a("code",[t._v("B")]),t._v(" has virtual base "),a("code",[t._v("A")]),t._v(" it means that "),a("code",[t._v("A")]),t._v(" "),a("strong",[t._v("will reside in most derived class")]),t._v(" of inheritance tree, and thus that most derived class is also responsible for initializing that virtual base:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" member"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("A")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" param"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        member "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" param"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("virtual")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")])]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("B")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("A")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("C")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")])]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("C")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/*A(88)*/")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("f")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    C object"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//error since C is not initializing it's indirect virtual base `A`")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("If we un-comment "),a("code",[t._v("/*A(88)*/")]),t._v(" we won't get any error since "),a("code",[t._v("C")]),t._v(" is now initializing it's indirect virtual base "),a("code",[t._v("A")]),t._v(".")]),t._v(" "),a("p",[t._v("Also note that when we're creating variable "),a("code",[t._v("object")]),t._v(", most derived class is "),a("code",[t._v("C")]),t._v(", so "),a("code",[t._v("C")]),t._v(" is responsible for creating(calling constructor of) "),a("code",[t._v("A")]),t._v(" and thus value of "),a("code",[t._v("A::member")]),t._v(" is "),a("code",[t._v("88")]),t._v(", not "),a("code",[t._v("5")]),t._v(" (as it would be if we were creating object of type "),a("code",[t._v("B")]),t._v(").")]),t._v(" "),a("p",[t._v("It is useful when solving the "),a("a",{attrs:{href:"https://en.wikipedia.org/wiki/Multiple_inheritance#The_diamond_problem",target:"_blank",rel:"noopener noreferrer"}},[t._v("diamond problem"),a("OutboundLink")],1),t._v(".:")]),t._v(" "),a("div",{staticClass:"language- extra-class"},[a("pre",{pre:!0,attrs:{class:"language-text"}},[a("code",[t._v("\n A                                        A   A\n / \\                                       |   |\nB   C                                      B   C\n \\ /                                        \\ /\n  D                                          D\nvirtual inheritance                   normal inheritance\n\n")])])]),a("p",[a("code",[t._v("B")]),t._v(" and "),a("code",[t._v("C")]),t._v(" both inherit from "),a("code",[t._v("A")]),t._v(", and "),a("code",[t._v("D")]),t._v(" inherits from "),a("code",[t._v("B")]),t._v(" and "),a("code",[t._v("C")]),t._v(", so "),a("strong",[t._v("there are 2 instances of "),a("code",[t._v("A")]),t._v(" in "),a("code",[t._v("D")]),t._v("!")]),t._v(" This results in ambiguity when you're accessing member of "),a("code",[t._v("A")]),t._v(" through "),a("code",[t._v("D")]),t._v(", as the compiler has no way of knowing from which class do you want to access that member (the one which "),a("code",[t._v("B")]),t._v(" inherits, or the one that is inherited by"),a("code",[t._v("C")]),t._v("?).")]),t._v(" "),a("p",[t._v("Virtual inheritance solves this problem: Since virtual base resides only in most derived object, there will be only one instance of "),a("code",[t._v("A")]),t._v(" in "),a("code",[t._v("D")]),t._v(".")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/*virtual*/")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("C")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/*virtual*/")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("D")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("C")])]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("bar")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//Error, which foo? B::foo() or C::foo()? - Ambiguous")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Removing the comments resolves the ambiguity.")]),t._v(" "),a("h2",{attrs:{id:"accessing-class-members"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#accessing-class-members"}},[t._v("#")]),t._v(" Accessing class members")]),t._v(" "),a("p",[t._v("To access member variables and member functions of an object of a class, the "),a("code",[t._v(".")]),t._v(" operator is used:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("SomeStruct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nSomeStruct var"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Accessing member variable a in var.")]),t._v("\nstd"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("cout "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" var"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("endl"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Assigning member variable b in var.")]),t._v("\nvar"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("b "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calling a member function.")]),t._v("\nvar"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("When accessing the members of a class via a pointer, the "),a("code",[t._v("->")]),t._v(" operator is commonly used.  Alternatively, the instance can be dereferenced and the "),a("code",[t._v(".")]),t._v(" operator used, although this is less common:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("SomeStruct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nSomeStruct var"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nSomeStruct "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v("p "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v("var"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Accessing member variable a in var via pointer.")]),t._v("\nstd"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("cout "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" p"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("->")]),t._v("a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("endl"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nstd"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("cout "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v("p"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("endl"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Assigning member variable b in var via pointer.")]),t._v("\np"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("->")]),t._v("b "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v("p"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("b "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calling a member function via a pointer.")]),t._v("\np"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("->")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v("p"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("When accessing static class members, the "),a("code",[t._v("::")]),t._v(" operator is used, but on the name of the class instead of an instance of it.  Alternatively, the static member can be accessed from an instance or a pointer to an instance using the "),a("code",[t._v(".")]),t._v(" or "),a("code",[t._v("->")]),t._v(" operator, respectively, with the same syntax as accessing non-static members.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("SomeStruct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" a"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("bar")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" SomeStruct"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nSomeStruct var"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nSomeStruct"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v(" p "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v("var"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Assigning static member variable c in struct SomeStruct.")]),t._v("\nSomeStruct"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("c "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Accessing static member variable c in struct SomeStruct, through var and p.")]),t._v("\nvar"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" var"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nvar"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("b "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" p"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("->")]),t._v("c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calling a static member function.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("SomeStruct")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("bar")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nvar"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("bar")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\np"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("->")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("bar")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("h3",{attrs:{id:"background"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#background"}},[t._v("#")]),t._v(" Background")]),t._v(" "),a("p",[t._v("The "),a("code",[t._v("->")]),t._v(" operator is needed because the member access operator "),a("code",[t._v(".")]),t._v(" has precedence over the dereferencing operator "),a("code",[t._v("*")]),t._v(".")]),t._v(" "),a("p",[t._v("One would expect that "),a("code",[t._v("*p.a")]),t._v(" would dereference "),a("code",[t._v("p")]),t._v(" (resulting in a reference to the object "),a("code",[t._v("p")]),t._v(" is pointing to) and then accessing its member "),a("code",[t._v("a")]),t._v(". But in fact, it tries to access the member "),a("code",[t._v("a")]),t._v(" of "),a("code",[t._v("p")]),t._v(" and then dereference it. I.e. "),a("code",[t._v("*p.a")]),t._v(" is equivalent to "),a("code",[t._v("*(p.a)")]),t._v(". In the example above, this would result in a compiler error because of two facts: First, "),a("code",[t._v("p")]),t._v(" is a pointer and does not have a member "),a("code",[t._v("a")]),t._v(". Second, "),a("code",[t._v("a")]),t._v(" is an integer and, thus, can't be dereferenced.")]),t._v(" "),a("p",[t._v("The uncommonly used solution to this problem would be to explicitly control the precedence: "),a("code",[t._v("(*p).a")])]),t._v(" "),a("p",[t._v("Instead, the "),a("code",[t._v("->")]),t._v(" operator is almost always used. It is a short-hand for first dereferencing the pointer and then accessing it. I.e. "),a("code",[t._v("(*p).a")]),t._v(" is exactly the same as "),a("code",[t._v("p->a")]),t._v(".")]),t._v(" "),a("p",[t._v("The "),a("code",[t._v("::")]),t._v(" operator is the scope operator, used in the same manner as accessing a member of a namespace.  This is because a static class member is considered to be in that class' scope, but isn't considered a member of instances of that class.  The use of normal "),a("code",[t._v(".")]),t._v(" and "),a("code",[t._v("->")]),t._v(" is also allowed for static members, despite them not being instance members, for historical reasons; this is of use for writing generic code in templates, as the caller doesn't need to be concerned with whether a given member function is static or non-static.")]),t._v(" "),a("h2",{attrs:{id:"private-inheritance-restricting-base-class-interface"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#private-inheritance-restricting-base-class-interface"}},[t._v("#")]),t._v(" Private inheritance: restricting base class interface")]),t._v(" "),a("p",[t._v("Private inheritance is useful when it is required to restrict the public interface of the class:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("move")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("turn")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("private")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("using")]),t._v(" A"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("turn"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" \n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nB b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nb"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("move")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// compile error")]),t._v("\nb"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("turn")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// OK")]),t._v("\n\n")])])]),a("p",[t._v("This approach efficiently prevents an access to the A public methods by casting to the A pointer or reference:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[t._v("B b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" \nA"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token generic-function"}},[a("span",{pre:!0,attrs:{class:"token function"}},[t._v("static_cast")]),a("span",{pre:!0,attrs:{class:"token generic class-name"}},[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("A"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")])])]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// compile error")]),t._v("\n\n")])])]),a("p",[t._v("In the case of public inheritance such casting will provide access to all the A public methods despite on alternative ways to prevent this in derived B, like hiding:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("private")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("move")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("  \n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("or private using:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("private")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("using")]),t._v(" A"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("move"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("  \n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("then for both cases it is possible:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[t._v("B b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nA"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" a "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token generic-function"}},[a("span",{pre:!0,attrs:{class:"token function"}},[t._v("static_cast")]),a("span",{pre:!0,attrs:{class:"token generic class-name"}},[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("A"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")])])]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("b"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// OK for public inheritance")]),t._v("\na"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("move")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// OK")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"nested-classes-structures"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#nested-classes-structures"}},[t._v("#")]),t._v(" Nested Classes/Structures")]),t._v(" "),a("p",[t._v("A "),a("code",[t._v("class")]),t._v(" or "),a("code",[t._v("struct")]),t._v(" can also contain another "),a("code",[t._v("class")]),t._v("/"),a("code",[t._v("struct")]),t._v(' definition inside itself, which is called a "nested class"; in this situation, the containing class is referred to as the "enclosing class".  The nested class definition is considered to be a member of the enclosing class, but is otherwise separate.')]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("From outside of the enclosing class, nested classes are accessed using the scope operator.  From inside the enclosing class, however, nested classes can be used without qualifiers:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    Inner in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\nOuter o"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nOuter"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("Inner i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" o"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("As with a non-nested "),a("code",[t._v("class")]),t._v("/"),a("code",[t._v("struct")]),t._v(", member functions and static variables can be defined either within a nested class, or in the enclosing namespace.  However, they cannot be defined within the enclosing class, due to it being considered to be a different class than the nested class.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Bad.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" Outer"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("As with non-nested classes, nested classes can be forward declared and defined later, provided they are defined before being used directly.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner2")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner1")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    Inner1 in1"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    Inner2"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v(" in2p"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("Outer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("~")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("Outer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner2")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("Outer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("in1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("Inner1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("in2p")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" Inner2"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("~")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("Outer")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("if")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("in2p"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("delete")]),t._v(" in2p"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("Prior to C++11, nested classes only had access to type names, "),a("code",[t._v("static")]),t._v(" members, and enumerators from the enclosing class; all other members defined in the enclosing class were off-limits.")]),t._v(" "),a("p",[t._v("As of C++11, nested classes, and members thereof, are treated as if they were "),a("code",[t._v("friend")]),t._v("s of the enclosing class, and can access all of its members, according to the usual access rules; if members of the nested class require the ability to evaluate one or more non-static members of the enclosing class, they must therefore be passed an instance:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("get_sizeof_x")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n            "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("sizeof")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Legal (C++11): x is unevaluated, so no instance is required.")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("get_x")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n            "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Illegal: Can't access non-static member without an instance.")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("get_x")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("Outer"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" o"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n            "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" o"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Legal (C++11): As a member of Outer, Inner can access private members.")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Conversely, the enclosing class is "),a("strong",[t._v("not")]),t._v(" treated as a friend of the nested class, and thus cannot access its private members without explicitly being granted permission.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// friend class Outer;")]),t._v("\n\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    Inner in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("get_x")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error: int Outer::Inner::x is private.")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// Uncomment "friend" line above to fix.')]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Friends of a nested class are not automatically considered friends of the enclosing class; if they need to be friends of the enclosing class as well, this must be declared separately.  Conversely, as the enclosing class is not automatically considered a friend of the nested class, neither will friends of the enclosing class be considered friends of the nested class.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("friend")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("barge_out")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("Outer"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" Inner"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("friend")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("barge_in")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("Outer"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" Inner"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" o"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("barge_in")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("Outer"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" Outer"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("Inner"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" o "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("o"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error: int Outer::o is private.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("barge_out")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("Outer"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" Outer"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("Inner"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error: int Outer::Inner::i is private.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" o "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" out"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("o"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("As with all other class members, nested classes can only be named from outside the class if they have public access.  However, you are allowed to access them regardless of access modifier, as long as you don't explicitly name them.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("cout "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"I have no private taboo.\\n"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" Inner "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("make_Inner")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("Inner")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\nOuter"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("Inner oi"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error: Outer::Inner is private.")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("auto")]),t._v(" oi "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("make_Inner")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\noi"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("                     "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("make_Inner")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n\n")])])]),a("p",[t._v("You can also create a type alias for a nested class.  If a type alias is contained in the enclosing class, the nested type and the type alias can have different access modifiers.  If the type alias is outside the enclosing class, it requires that either the nested class, or a "),a("code",[t._v("typedef")]),t._v(" thereof, be public.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner_")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" Inner_ Inner"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" Outer"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("Inner  ImOut"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" Outer"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("Inner_ ImBad"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\nOuter"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("Inner  oi"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\nOuter"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("Inner_ oi"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\nImOut         oi"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n\n")])])]),a("p",[t._v("As with other classes, nested classes can both derive from or be derived from by other classes.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Base")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Outer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Base")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Derived")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[t._v("Outer"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("This can be useful in situations where the enclosing class is derived from by another class, by allowing the programmer to update the nested class as necessary.  This can be combined with a typedef to provide a consistent name for each enclosing class' nested class:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("BaseOuter")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("BaseInner_")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("virtual")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("virtual")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something_else")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" b_in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" BaseInner_ Inner"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("virtual")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("~")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("BaseOuter")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("default")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("virtual")]),t._v(" Inner"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("getInner")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" b_in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" BaseOuter"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("BaseInner_")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something_else")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ---")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("DerivedOuter")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("BaseOuter")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Note the use of the qualified typedef; BaseOuter::BaseInner_ is private.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("DerivedInner_")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[t._v("BaseOuter"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Inner")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("override")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something_else")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("override")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" d_in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" DerivedInner_ Inner"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    BaseOuter"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("Inner"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("getInner")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("override")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" d_in"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" DerivedOuter"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("DerivedInner_")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something_else")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calls BaseOuter::BaseInner_::do_something();")]),t._v("\nBaseOuter"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v(" b "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" BaseOuter"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nBaseOuter"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("Inner"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" bin "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" b"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("->")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("getInner")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nbin"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nb"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("->")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("getInner")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calls DerivedOuter::DerivedInner_::do_something();")]),t._v("\nBaseOuter"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v(" d "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" DerivedOuter"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nBaseOuter"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("Inner"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" din "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" d"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("->")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("getInner")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\ndin"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nd"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("->")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("getInner")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("do_something")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("In the above case, both "),a("code",[t._v("BaseOuter")]),t._v(" and "),a("code",[t._v("DerivedOuter")]),t._v(" supply the member type "),a("code",[t._v("Inner")]),t._v(", as "),a("code",[t._v("BaseInner_")]),t._v(" and "),a("code",[t._v("DerivedInner_")]),t._v(", respectively.  This allows nested types to be derived without breaking the enclosing class' interface, and allows the nested type to be used polymorphically.")]),t._v(" "),a("h2",{attrs:{id:"member-types-and-aliases"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#member-types-and-aliases"}},[t._v("#")]),t._v(" Member Types and Aliases")]),t._v(" "),a("p",[t._v("A "),a("code",[t._v("class")]),t._v(" or "),a("code",[t._v("struct")]),t._v(" can also define member type aliases, which are type aliases contained within, and treated as members of, the class itself.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("IHaveATypedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" MyTypedef"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("IHaveATemplateTypedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("template")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typename")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("using")]),t._v(" MyTemplateTypedef "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("vector"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("T"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Like static members, these typedefs are accessed using the scope operator, "),a("code",[t._v("::")]),t._v(".")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[t._v("IHaveATypedef"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("MyTypedef i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// i is an int.")]),t._v("\n\nIHaveATemplateTypedef"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("MyTemplateTypedef"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" v"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// v is a std::vector<int>.")]),t._v("\n\n")])])]),a("p",[t._v("As with normal type aliases, each member type alias is allowed to refer to any type defined or aliased before, but not after, its definition.  Likewise, a typedef outside the class definition can refer to any accessible typedefs within the class definition, provided it comes after the class definition.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("template")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typename")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Helper")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    T "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("get")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token generic-function"}},[a("span",{pre:!0,attrs:{class:"token function"}},[t._v("static_cast")]),a("span",{pre:!0,attrs:{class:"token generic class-name"}},[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("T"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")])])]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("42")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("IHaveTypedefs")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//    typedef MyTypedef NonLinearTypedef; // Error if uncommented.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" MyTypedef"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" Helper"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("MyTypedef"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" MyTypedefHelper"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nIHaveTypedefs"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("MyTypedef        i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// x_i is an int.")]),t._v("\nIHaveTypedefs"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("MyTypedefHelper hi"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// x_hi is a Helper<int>.")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" IHaveTypedefs"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("MyTypedef TypedefBeFree"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nTypedefBeFree ii"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("                  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ii is an int.")]),t._v("\n\n")])])]),a("p",[t._v("Member type aliases can be declared with any access level, and will respect the appropriate access modifier.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("TypedefAccessLevels")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" PrvInt"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("protected")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" ProInt"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" PubInt"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nTypedefAccessLevels"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("PrvInt prv_i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error: TypedefAccessLevels::PrvInt is private.")]),t._v("\nTypedefAccessLevels"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("ProInt pro_i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error: TypedefAccessLevels::ProInt is protected.")]),t._v("\nTypedefAccessLevels"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("PubInt pub_i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Derived")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("TypedefAccessLevels")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    PrvInt prv_i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error: TypedefAccessLevels::PrvInt is private.")]),t._v("\n    ProInt pro_i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n    PubInt pub_i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("This can be used to provide a level of abstraction, allowing a class' designer to change its internal workings without breaking code that relies on it.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Something")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("friend")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("SomeComplexType")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("short")]),t._v(" s"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" SomeComplexType MyHelper"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    MyHelper "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("get_helper")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("MyHelper")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("8")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" s"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("19.5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"shoe"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token boolean"}},[t._v("false")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\nSomething s"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nSomething"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("MyHelper hlp "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" s"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("get_helper")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("In this situation, if the helper class is changed from "),a("code",[t._v("SomeComplexType")]),t._v(" to some other type, only the "),a("code",[t._v("typedef")]),t._v(" and the "),a("code",[t._v("friend")]),t._v(" declaration would need to be modified; as long as the helper class provides the same functionality, any code that uses it as "),a("code",[t._v("Something::MyHelper")]),t._v(" instead of specifying it by name will usually still work without any modifications.  In this manner, we minimise the amount of code that needs to be modified when the underlying implementation is changed, such that the type name only needs to be changed in one location.")]),t._v(" "),a("p",[t._v("This can also be combined with "),a("code",[t._v("decltype")]),t._v(", if one so desires.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("SomethingElse")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    AnotherComplexType"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("bool")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" SomeThirdClass"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" helper"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("decltype")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("helper"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" MyHelper"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("private")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    InternalVariable"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("MyHelper"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" ivh"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    MyHelper"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("get_helper")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" helper"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("In this situation, changing the implementation of "),a("code",[t._v("SomethingElse::helper")]),t._v(" will automatically change the typedef for us, due to "),a("code",[t._v("decltype")]),t._v(".  This minimises the number of modifications necessary when we want to change "),a("code",[t._v("helper")]),t._v(", which minimises the risk of human error.")]),t._v(" "),a("p",[t._v("As with everything, however, this can be taken too far.  If the typename is only used once or twice internally and zero times externally, for example, there's no need to provide an alias for it.  If it's used hundreds or thousands of times throughout a project, or if it has a long enough name, then it can be useful to provide it as a typedef instead of always using it in absolute terms.  One must balance forwards compatibility and convenience with the amount of unnecessary noise created.")]),t._v(" "),a("p",[t._v("This can also be used with template classes, to provide access to the template parameters from outside the class.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("template")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typename")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("SomeClass")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" T MyParam"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    MyParam "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("getParam")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token generic-function"}},[a("span",{pre:!0,attrs:{class:"token function"}},[t._v("static_cast")]),a("span",{pre:!0,attrs:{class:"token generic class-name"}},[a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("T"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")])])]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("42")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("template")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typename")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typename")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("MyParam "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("some_func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("T"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" t"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" t"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("getParam")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\nSomeClass"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" si"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("some_func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("si"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("This is commonly used with containers, which will usually provide their element type, and other helper types, as member type aliases.  Most of the containers in the C++ standard library, for example, provide the following 12 helper types, along with any other special types they might need.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("template")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typename")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("SomeContainer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Let's provide the same helper types as most standard containers.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" T                                     value_type"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("allocator"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("value_type"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("            allocator_type"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" value_type"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v("                           reference"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" value_type"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v("                     const_reference"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" value_type"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v("                           pointer"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" value_type"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v("                     const_pointer"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" MyIterator"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("value_type"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("                iterator"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" MyConstIterator"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("value_type"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("           const_iterator"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("reverse_iterator"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("iterator"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("       reverse_iterator"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("reverse_iterator"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("const_iterator"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" const_reverse_iterator"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" size_t                                size_type"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" ptrdiff_t                             difference_type"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v('Prior to C++11, it was also commonly used to provide a "template '),a("code",[t._v("typedef")]),t._v("\" of sorts, as the feature wasn't yet available; these have become a bit less common with the introduction of alias templates, but are still useful in some situations (and are combined with alias templates in other situations, which can be very useful for obtaining individual components of a complex type such as a function pointer).  They commonly use the name "),a("code",[t._v("type")]),t._v(" for their type alias.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("template")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typename")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("TemplateTypedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" T type"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\nTemplateTypedef"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("type i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// i is an int.")]),t._v("\n\n")])])]),a("p",[t._v("This was often used with types with multiple template parameters, to provide an alias that defines one or more of the parameters.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("template")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typename")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" size_t SZ"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" size_t D"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Array")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/* ... */")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("template")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typename")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" size_t SZ"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("OneDArray")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" Array"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("T"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" SZ"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" type"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("template")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typename")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" size_t SZ"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("TwoDArray")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" Array"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("T"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" SZ"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" type"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("template")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typename")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("T")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("MonoDisplayLine")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" Array"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),t._v("T"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("80")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),t._v(" type"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nOneDArray"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("3")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("type     arr1i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// arr1i is an Array<int, 3, 1>.")]),t._v("\nTwoDArray"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("short")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("type   arr2s"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// arr2s is an Array<short, 5, 2>.")]),t._v("\nMonoDisplayLine"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("char")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(">")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("type arr3c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// arr3c is an Array<char, 80, 1>.")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"multiple-inheritance"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#multiple-inheritance"}},[t._v("#")]),t._v(" Multiple Inheritance")]),t._v(" "),a("p",[t._v("Aside from single inheritance:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("You can also have multiple inheritance:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("C")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("A")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("B")])]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[a("code",[t._v("C")]),t._v(" will now have inherit from "),a("code",[t._v("A")]),t._v(" and "),a("code",[t._v("B")]),t._v(" at the same time.")]),t._v(" "),a("p",[a("em",[a("strong",[t._v("Note: this can lead to ambiguity if the same names are used in multiple inherited "),a("code",[t._v("class")]),t._v("s or "),a("code",[t._v("struct")]),t._v("s. Be careful!")])])]),t._v(" "),a("p",[t._v("*Ambiguity in Multiple Inheritance *")]),t._v(" "),a("p",[t._v("Multiple inheritance may be helpful in certain cases but, sometimes odd sort of problem encounters while using multiple inheritance.")]),t._v(" "),a("p",[t._v("For example: Two base classes have functions with same name which is not overridden in derived class and if you write code to access that function using object of derived class, compiler shows error because, it cannot determine which function to call. Here is a code for this type of ambiguity in multiple inheritance.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("base1")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n     "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("funtion")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n     "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//code for base1 function }  ")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("base2")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n     "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// code for base2 function } ")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("derived")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token base-clause"}},[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("base1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("base2")])]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    \n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    derived obj"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    \n  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error because compiler can't figure out which function to call ")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//either function( ) of base1 or base2 .   ")]),t._v("\n    obj"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("  \n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("But, this problem can be solved using scope resolution function to specify which function to class either base1 or base2:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("main")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    obj"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("base1"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Function of class base1 is called. ")]),t._v("\n    obj"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("base2"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Function of class base2 is called.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("h2",{attrs:{id:"static-class-members"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#static-class-members"}},[t._v("#")]),t._v(" Static class members")]),t._v(" "),a("p",[t._v("A class is also allowed to have "),a("code",[t._v("static")]),t._v(" members, which can be either variables or functions.  These are considered to be in the class' scope, but aren't treated as normal members; they have static storage duration (they exist from the start of the program to the end), aren't tied to a particular instance of the class, and only one copy exists for the entire class.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Example")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" num_instances"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("      "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Static data member (static member variable).")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("                         "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Non-static member variable.")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("string static_str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Static data member (static member variable).")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("static_func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("      "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Static member function.")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Non-static member functions can modify static member variables.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("Example")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("++")]),t._v("num_instances"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("set_str")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("string"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v("         Example"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("num_instances"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nstd"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("string Example"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("static_str "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Hello."')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\nExample one"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" two"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" three"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// Each Example has its own "i", such that:')]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//  (&one.i != &two.i)")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//  (&one.i != &three.i)")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//  (&two.i != &three.i).")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v('// All three Examples share "num_instances", such that:')]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//  (&one.num_instances == &two.num_instances)")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//  (&one.num_instances == &three.num_instances)")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("//  (&two.num_instances == &three.num_instances)")]),t._v("\n\n")])])]),a("p",[t._v("Static member variables are not considered to be defined inside the class, only declared, and thus have their definition outside the class definition; the programmer is allowed, but not required, to initialise static variables in their definition.  When defining the member variables, the keyword "),a("code",[t._v("static")]),t._v(" is omitted.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Example")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" num_instances"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("               "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Declaration.")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("string static_str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("          "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Declaration.")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v("         Example"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("num_instances"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("         "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Definition.  Zero-initialised.")]),t._v("\nstd"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("string Example"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("static_str "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"Hello."')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Definition.")]),t._v("\n\n")])])]),a("p",[t._v("Due to this, static variables can be incomplete types (apart from "),a("code",[t._v("void")]),t._v("), as long as they're later defined as a complete type.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ForwardDeclared")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ExIncomplete")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" ForwardDeclared fd"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" ExIncomplete    i_contain_myself"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v("             an_array"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ForwardDeclared")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nForwardDeclared ExIncomplete"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("fd"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nExIncomplete    ExIncomplete"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("i_contain_myself"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v("             ExIncomplete"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("an_array"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Static member functions can be defined inside or outside the class definition, as with normal member functions.  As with static member variables, the keyword "),a("code",[t._v("static")]),t._v(" is omitted when defining static member functions outside the class definition.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// For Example above, either...")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Example")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("static_func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" num_instances"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("set_str")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("string"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" static_str "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Or...")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Example")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/* ... */")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Example")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("static_func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" num_instances"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Example")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("set_str")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("string"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" static_str "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("If a static member variable is declared "),a("code",[t._v("const")]),t._v(" but not "),a("code",[t._v("volatile")]),t._v(", and is of an integral or enumeration type, it can be initialised at declaration, inside the class definition.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("enum")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("E")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" VAL "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ExConst")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" ci "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("              "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" E ce "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" VAL"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("              "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("double")]),t._v(" cd "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("           "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("volatile")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" cvi "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("double")]),t._v(" good_cd"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("volatile")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" good_cvi"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("double")]),t._v(" ExConst"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("good_cd "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("        "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("volatile")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" ExConst"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("good_cvi "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n\n")])])]),a("p",[t._v("As of C++11, static member variables of "),a("code",[t._v("LiteralType")]),t._v(" types (types that can be constructed at compile time, according to "),a("code",[t._v("constexpr")]),t._v(" rules) can also be declared as "),a("code",[t._v("constexpr")]),t._v("; if so, they must be initialised within the class definition.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ExConstexpr")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("constexpr")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" ci "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("                      "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("constexpr")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("double")]),t._v(" cd "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("                   "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("constexpr")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" carr"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("2")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("        "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("constexpr")]),t._v(" ConstexprConstructibleClass c"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("constexpr")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" bad_ci"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("                      "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("constexpr")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" ExConstexpr"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("bad_ci "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("                "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Still an error.")]),t._v("\n\n")])])]),a("p",[t._v("If a "),a("code",[t._v("const")]),t._v(" or "),a("code",[t._v("constexpr")]),t._v(" static member variable is "),a("strong",[t._v("odr-used")]),t._v(" (informally, if it has its address taken or is assigned to a reference), then it must still have a separate definition, outside the class definition.  This definition is not allowed to contain an initialiser.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ExODR")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" odr_used "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// const int ExODR::odr_used;")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v(" odr_user "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" ExODR"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("odr_used"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error; uncomment above line to resolve.")]),t._v("\n\n")])])]),a("p",[t._v("As static members aren't tied to a given instance, they can be accessed using the scope operator, "),a("code",[t._v("::")]),t._v(".")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[t._v("std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("string str "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" Example"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("static_str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("They can also be accessed as if they were normal, non-static members.  This is of historical significance, but is used less commonly than the scope operator to prevent confusion over whether a member is static or non-static.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[t._v("Example ex"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nstd"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("string rts "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" ex"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("static_str"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Class members are able to access static members without qualifying their scope, as with non-static class members.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ExTwo")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" num_instances"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" my_num"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("ExTwo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("my_num")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("num_instances"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("++")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("get_total_instances")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" num_instances"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("get_instance_number")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("return")]),t._v(" my_num"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" ExTwo"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("num_instances"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("They cannot be "),a("code",[t._v("mutable")]),t._v(", nor would they need to be; as they aren't tied to any given instance, whether an instance is or isn't const doesn't affect static members.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ExDontNeedMutable")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" immuta"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("mutable")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" muta"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("ExDontNeedMutable")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("immuta")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("muta")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" ExDontNeedMutable"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" ExDontNeedMutable dnm"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\ndnm"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("immuta "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error: Can't modify read-only object.")]),t._v("\ndnm"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("muta "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("   "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.  Mutable fields of const objects can be written.")]),t._v("\ndnm"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("      "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.  Static members can be written regardless of an instance's const-ness.")]),t._v("\n\n")])])]),a("p",[t._v("Static members respect access modifiers, just like non-static members.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ExAccess")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" prv_int"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("protected")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" pro_int"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" pub_int"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" ExAccess"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("prv_int"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" ExAccess"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("pro_int"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" ExAccess"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("pub_int"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// ...")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" x1 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" ExAccess"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("prv_int"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error: int ExAccess::prv_int is private.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" x2 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" ExAccess"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("pro_int"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error: int ExAccess::pro_int is protected.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" x3 "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" ExAccess"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("pub_int"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n\n")])])]),a("p",[t._v("As they aren't tied to a given instance, static member functions have no "),a("code",[t._v("this")]),t._v(" pointer; due to this, they can't access non-static member variables unless passed an instance.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ExInstanceRequired")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("int")]),t._v(" i"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("ExInstanceRequired")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("i")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("bad_mutate")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("++")]),t._v("i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("                         "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("good_mutate")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("ExInstanceRequired"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("++")]),t._v("e"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("i "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("5")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Due to not having a "),a("code",[t._v("this")]),t._v(" pointer, their addresses can't be stored in pointers-to-member-functions, and are instead stored in normal pointers-to-functions.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ExPointer")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n           "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("nsfunc")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("sfunc")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("ExPointer"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v(" mem_f_ptr"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("typedef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v("f_ptr"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nmem_f_ptr p_sf "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v("ExPointer"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("sfunc"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n    f_ptr p_sf "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v("ExPointer"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("sfunc"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n\n")])])]),a("p",[t._v("Due to not having a "),a("code",[t._v("this")]),t._v(" pointer, they also cannot be "),a("code",[t._v("const")]),t._v(" or "),a("code",[t._v("volatile")]),t._v(", nor can they have ref-qualifiers.  They also cannot be virtual.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ExCVQualifiersAndVirtual")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v("   "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("                "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Good.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("cfunc")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v("          "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("vfunc")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("volatile")]),t._v("       "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("cvfunc")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("volatile")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("rfunc")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v("              "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("rvfunc")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&&")]),t._v("             "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("virtual")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("vsfunc")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("        "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("static")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("virtual")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("svfunc")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("        "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Error.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("As they aren't tied to a given instance, static member variables are effectively treated as special global variables; they're created when the program starts, and destroyed when it exits, regardless of whether any instances of the class actually exist.  Only a single copy of each static member variable exists (unless the variable is declared "),a("code",[t._v("thread_local")]),t._v(" (C++11 or later), in which case there's one copy per thread).")]),t._v(" "),a("p",[t._v("Static member variables have the same linkage as the class, whether the class has external or internal linkage.  Local classes and unnamed classes aren't allowed to have static members.")]),t._v(" "),a("h2",{attrs:{id:"non-static-member-functions"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#non-static-member-functions"}},[t._v("#")]),t._v(" Non-static member functions")]),t._v(" "),a("p",[t._v("A class can have "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/c%2B%2B/5661/non-static-member-functions",target:"_blank",rel:"noopener noreferrer"}},[t._v("non-static member functions"),a("OutboundLink")],1),t._v(", which operate on individual instances of the class.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("class")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("CL")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n  "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("public")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("member_function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("These functions are called on an instance of the class, like so:")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[t._v("CL instance"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\ninstance"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("member_function")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("They can be defined either inside or outside the class definition; if defined outside, they are specified as being in the class' scope.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ST")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("defined_inside")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("defined_outside")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("ST")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("defined_outside")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("They can be "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/c%2B%2B/7146/the-this-pointer/24492/this-pointer-cv-qualifiers#t=201610150101175922343",target:"_blank",rel:"noopener noreferrer"}},[t._v("CV-qualified"),a("OutboundLink")],1),t._v(" and/or "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/c%2B%2B/7146/the-this-pointer/24493/this-pointer-ref-qualifiers#t=201610150101354472159",target:"_blank",rel:"noopener noreferrer"}},[t._v("ref-qualified"),a("OutboundLink")],1),t._v(", affecting how they see the instance they're called upon; the function will see the instance as having the specified cv-qualifier(s), if any.  Which version is called will be based on the instance's cv-qualifiers.  If there is no version with the same cv-qualifiers as the instance, then a more-cv-qualified version will be called if available.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("CVQualifiers")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("                   "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 1: Instance is non-cv-qualified.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v("             "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 2: Instance is const.")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("cv_only")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("volatile")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nCVQualifiers       non_cv_instance"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" CVQualifiers      c_instance"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nnon_cv_instance"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calls #1.")]),t._v("\nc_instance"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("      "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calls #2.")]),t._v("\n\nnon_cv_instance"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("cv_only")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calls const volatile version.")]),t._v("\nc_instance"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("cv_only")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("      "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calls const volatile version.")]),t._v("\n\n")])])]),a("p",[t._v("Member function ref-qualifiers indicate whether or not the function is intended to be called on rvalue instances, and use the same syntax as function cv-qualifiers.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("RefQualifiers")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v("  "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 1: Called on normal instances.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&&")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// 2: Called on rvalue (temporary) instances.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nRefQualifiers rf"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nrf"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("              "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calls #1.")]),t._v("\nRefQualifiers"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calls #2.")]),t._v("\n\n")])])]),a("p",[t._v("CV-qualifiers and ref-qualifiers can also be combined if necessary.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("BothCVAndRef")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Called on normal instances.  Sees instance as const.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&&")]),t._v("     "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Called on temporary instances.")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("They can also be "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/c%2B%2B/1752/virtual-member-functions",target:"_blank",rel:"noopener noreferrer"}},[t._v("virtual"),a("OutboundLink")],1),t._v("; this is fundamental to polymorphism, and allows a child class(es) to provide the same interface as the parent class, while supplying their own functionality.")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Base")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("virtual")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Derived")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("virtual")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nBase"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v(" bp "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" Base"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nBase"),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("*")]),t._v(" dp "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("new")]),t._v(" Derived"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\nbp"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calls Base::func().")]),t._v("\ndp"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("func")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// Calls Derived::func().")]),t._v("\n\n")])])]),a("p",[t._v("For more information, see "),a("a",{attrs:{href:"http://stackoverflow.com/documentation/c%2B%2B/5661/non-static-member-functions",target:"_blank",rel:"noopener noreferrer"}},[t._v("here"),a("OutboundLink")],1),t._v(".")]),t._v(" "),a("h2",{attrs:{id:"unnamed-struct-class"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#unnamed-struct-class"}},[t._v("#")]),t._v(" Unnamed struct/class")]),t._v(" "),a("p",[a("strong",[t._v("Unnamed "),a("code",[t._v("struct")])]),t._v(" is allowed (type has no name)")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("foo")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/* No name */")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("float")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("float")]),t._v(" y"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" point"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    \n    point"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("42")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])]),a("p",[t._v("or")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("Circle")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/* No name */")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("float")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("float")]),t._v(" y"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" center"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// but a member name")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("float")]),t._v(" radius"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("and later")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[t._v("Circle circle"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\ncircle"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("center"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("42.f")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("but NOT "),a("strong",[t._v("anonymous "),a("code",[t._v("struct")])]),t._v(" (unnamed type and unnamed object)")]),t._v(" "),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("InvalidCircle")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("/* No name */")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("float")]),t._v(" centerX"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("float")]),t._v(" centerY"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// No member either.")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("float")]),t._v(" radius"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])]),a("p",[t._v("Note: Some compilers allow "),a("strong",[t._v("anonymous "),a("code",[t._v("struct")])]),t._v(" as "),a("strong",[t._v("extension")]),t._v(".")]),t._v(" "),a("li",[t._v("\n**lamdba** can be seen as a special **unnamed `struct`**.\n")]),t._v(" "),a("li",[t._v("\n`decltype` allows to retrieve the type of **unnamed `struct`**:\n"),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("decltype")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("circle"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("point"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" otherPoint"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n")])])])]),t._v(" "),a("li",[t._v("\n**unnamed `struct`** instance can be parameter of template method:\n"),a("div",{staticClass:"language-cpp extra-class"},[a("pre",{pre:!0,attrs:{class:"language-cpp"}},[a("code",[a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("print_square_coordinates")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("struct")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("float")]),t._v(" x"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("float")]),t._v(" y"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v(" points"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v("\n        "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("-")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token comment"}},[t._v("// for range relies on `template <class T, std::size_t N> std::begin(T (&)[N])`")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("for")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("const")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("auto")]),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("&")]),t._v(" point "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v(":")]),t._v(" points"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),t._v(" \n        std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("cout "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"{"')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" point"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("x "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('", "')]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" point"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(".")]),t._v("y "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"}\\n"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("decltype")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("points"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("[")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("0")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("]")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" topRightCorner"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("{")]),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    "),a("span",{pre:!0,attrs:{class:"token keyword"}},[t._v("auto")]),t._v(" it "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("=")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("find")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("points"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" points "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("4")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" topRightCorner"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n    std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),t._v("cout "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"top right corner is the "')]),t._v("\n              "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token number"}},[t._v("1")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("+")]),t._v(" std"),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[t._v("::")]),a("span",{pre:!0,attrs:{class:"token function"}},[t._v("distance")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("(")]),t._v("points"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(",")]),t._v(" it"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(")")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token operator"}},[t._v("<<")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token string"}},[t._v('"th\\n"')]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n"),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v("}")]),t._v("\n\n")])])])]),t._v(" "),a("h4",{attrs:{id:"syntax"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#syntax"}},[t._v("#")]),t._v(" Syntax")]),t._v(" "),a("ul",[a("li",[t._v("variable.member_var = constant;")]),t._v(" "),a("li",[t._v("variable.member_function();")]),t._v(" "),a("li",[t._v("variable_pointer->member_var = constant;")]),t._v(" "),a("li",[t._v("variable_pointer->member_function();")])]),t._v(" "),a("h4",{attrs:{id:"remarks"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#remarks"}},[t._v("#")]),t._v(" Remarks")]),t._v(" "),a("p",[t._v("Note that the "),a("strong",[a("strong",[t._v("only")])]),t._v(" difference between the "),a("code",[t._v("struct")]),t._v(" and "),a("code",[t._v("class")]),t._v(" keywords is that by default, the member variables, member functions, and base classes of a "),a("code",[t._v("struct")]),t._v(" are "),a("code",[t._v("public")]),t._v(", while in a "),a("code",[t._v("class")]),t._v(" they are "),a("code",[t._v("private")]),t._v(". C++ programmers tend to call it a class if it has constructors and destructors, and the ability to enforce its own invariants; or a struct if it's just a simple collection of values, but the C++ language itself makes no distinction.")])])}),[],!1,null,null,null);s.default=e.exports}}]);