(window.webpackJsonp=window.webpackJsonp||[]).push([[757],{1165: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:"virtual-member-functions"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#virtual-member-functions"}},[t._v("#")]),t._v(" Virtual Member Functions")]),t._v(" "),a("h2",{attrs:{id:"using-override-with-virtual-in-c-11-and-later"}},[a("a",{staticClass:"header-anchor",attrs:{href:"#using-override-with-virtual-in-c-11-and-later"}},[t._v("#")]),t._v(" Using override with virtual in C++11 and later")]),t._v(" "),a("p",[t._v("The specifier "),a("code",[t._v("override")]),t._v(" has a special meaning in C++11 onwards, if appended at the end of function signature. This signifies that a function is")]),t._v(" "),a("ul",[a("li",[t._v("Overriding the function present in base class &")]),t._v(" "),a("li",[t._v("The Base class function is "),a("code",[t._v("virtual")])])]),t._v(" "),a("p",[t._v("There is no "),a("code",[t._v("run time")]),t._v(" significance of this specifier as is mainly meant as an indication for compilers")]),t._v(" "),a("p",[t._v("The example below will demonstrate the change in behaviour with our without using override.")]),t._v(" "),a("p",[t._v("Without "),a("code",[t._v("override")]),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 macro property"}},[a("span",{pre:!0,attrs:{class:"token directive-hash"}},[t._v("#")]),a("span",{pre:!0,attrs:{class:"token directive keyword"}},[t._v("include")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token 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Classes with one or more pure virtual functions are considered to be abstract, and cannot be instantiated; only derived classes which define, or inherit definitions for, all pure virtual functions can be instantiated.")]),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("Abstract")]),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("f")]),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("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\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("Concrete")]),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("f")]),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 punctuation"}},[t._v("}")]),a("span",{pre:!0,attrs:{class:"token punctuation"}},[t._v(";")]),t._v("\n\nAbstract a"),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("\nConcrete c"),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("Even if a function is specified as pure virtual, it can be given a default implementation.  Despite this, the function will still be considered abstract, and derived classes will have to define it before they can be instantiated.  In this case, the derived class' version of the function is even allowed to call the base class' version.")]),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("DefaultAbstract")]),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("f")]),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("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("void")]),t._v(" "),a("span",{pre:!0,attrs:{class:"token class-name"}},[t._v("DefaultAbstract")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[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(" "),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("WhyWouldWeDoThis")]),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("DefaultAbstract")])]),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("f")]),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 class-name"}},[t._v("DefaultAbstract")]),a("span",{pre:!0,attrs:{class:"token double-colon punctuation"}},[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(")")]),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("There are a couple of reasons why we might want to do this:")]),t._v(" "),a("li",[t._v("\nIf we want to create a class that can't itself be instantiated, but doesn't prevent its derived classes from being instantiated, we can declare the destructor as pure virtual.  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