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class="sidebar-link">Refactoring Techniques</a></li><li><a href="/cpp/internationalization-in-c.html" class="sidebar-link">Internationalization in C++</a></li><li><a href="/cpp/contributors.html" class="sidebar-link">The Contributors</a></li></ul></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h1 id="literals"><a href="#literals" class="header-anchor">#</a> Literals</h1> <p>Traditionally, a literal is an expression denoting a constant whose type and value are evident from its spelling. For example, <code>42</code> is a literal, while <code>x</code> is not since one must see its declaration to know its type and read previous lines of code to know its value.</p> <p>However, C++11 also added <a href="http://stackoverflow.com/documentation/c%2b%2b/2745/user-defined-literals" target="_blank" rel="noopener noreferrer">user-defined literals<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a>, which are not literals in the traditional sense but can be used as a shorthand for function calls.</p> <h2 id="true"><a href="#true" class="header-anchor">#</a> true</h2> <p>A <a href="http://stackoverflow.com/documentation/c%2b%2b/4891/keywords" target="_blank" rel="noopener noreferrer">keyword<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> denoting one of the two possible values of type <code>bool</code>.</p> <div class="language-cpp extra-class"><pre class="language-cpp"><code><span class="token keyword">bool</span> ok <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">f</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
ok <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
<span class="token keyword">goto</span> end<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><h2 id="false"><a href="#false" class="header-anchor">#</a> false</h2> <p>A <a href="http://stackoverflow.com/documentation/c%2b%2b/4891/keywords" target="_blank" rel="noopener noreferrer">keyword<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> denoting one of the two possible values of type <code>bool</code>.</p> <div class="language-cpp extra-class"><pre class="language-cpp"><code><span class="token keyword">bool</span> ok <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token operator">!</span><span class="token function">f</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
ok <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span>
<span class="token keyword">goto</span> end<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><h2 id="nullptr"><a href="#nullptr" class="header-anchor">#</a> nullptr</h2> <p>A <a href="http://stackoverflow.com/documentation/c%2b%2b/4891/keywords" target="_blank" rel="noopener noreferrer">keyword<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> denoting a null pointer constant. It can be converted to any pointer or pointer-to-member type, yielding a null pointer of the resulting type.</p> <div class="language-cpp extra-class"><pre class="language-cpp"><code>Widget<span class="token operator">*</span> p <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token function">Widget</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">delete</span> p<span class="token punctuation">;</span>
p <span class="token operator">=</span> <span class="token keyword">nullptr</span><span class="token punctuation">;</span> <span class="token comment">// set the pointer to null after deletion</span>
</code></pre></div><p>Note that <code>nullptr</code> is not itself a pointer. The type of <code>nullptr</code> is a fundamental type known as <code>std::nullptr_t</code>.</p> <div class="language-cpp extra-class"><pre class="language-cpp"><code><span class="token keyword">void</span> <span class="token function">f</span><span class="token punctuation">(</span><span class="token keyword">int</span><span class="token operator">*</span> p<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">template</span> <span class="token operator"><</span><span class="token keyword">class</span> <span class="token class-name">T</span><span class="token operator">></span>
<span class="token keyword">void</span> <span class="token function">g</span><span class="token punctuation">(</span>T<span class="token operator">*</span> p<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">void</span> <span class="token function">h</span><span class="token punctuation">(</span>std<span class="token double-colon punctuation">::</span>nullptr_t p<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">int</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token function">f</span><span class="token punctuation">(</span><span class="token keyword">nullptr</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// ok</span>
<span class="token function">g</span><span class="token punctuation">(</span><span class="token keyword">nullptr</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// error</span>
<span class="token function">h</span><span class="token punctuation">(</span><span class="token keyword">nullptr</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// ok</span>
<span class="token punctuation">}</span>
</code></pre></div><h2 id="this"><a href="#this" class="header-anchor">#</a> this</h2> <p>Within a member function of a class, the <a href="http://stackoverflow.com/documentation/c%2b%2b/4891/keywords" target="_blank" rel="noopener noreferrer">keyword<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> <code>this</code> is a pointer to the instance of the class on which the function was called. <code>this</code> cannot be used in a static member function.</p> <div class="language-cpp extra-class"><pre class="language-cpp"><code><span class="token keyword">struct</span> <span class="token class-name">S</span> <span class="token punctuation">{</span>
<span class="token keyword">int</span> x<span class="token punctuation">;</span>
S<span class="token operator">&</span> <span class="token keyword">operator</span><span class="token operator">=</span><span class="token punctuation">(</span><span class="token keyword">const</span> S<span class="token operator">&</span> other<span class="token punctuation">)</span> <span class="token punctuation">{</span>
x <span class="token operator">=</span> other<span class="token punctuation">.</span>x<span class="token punctuation">;</span>
<span class="token comment">// return a reference to the object being assigned to</span>
<span class="token keyword">return</span> <span class="token operator">*</span><span class="token keyword">this</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre></div><p>The type of <code>this</code> depends on the cv-qualification of the member function: if <code>X::f</code> is <code>const</code>, then the type of <code>this</code> within <code>f</code> is <code>const X*</code>, so <code>this</code> cannot be used to modify non-static data members from within a <code>const</code> member function. Likewise, <code>this</code> inherits <code>volatile</code> qualification from the function it appears in.</p> <p><code>this</code> can also be used in a <strong>brace-or-equal-initializer</strong> for a non-static data member.</p> <div class="language-cpp extra-class"><pre class="language-cpp"><code><span class="token keyword">struct</span> <span class="token class-name">S</span><span class="token punctuation">;</span>
<span class="token keyword">struct</span> <span class="token class-name">T</span> <span class="token punctuation">{</span>
<span class="token function">T</span><span class="token punctuation">(</span><span class="token keyword">const</span> S<span class="token operator">*</span> s<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// ...</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token keyword">struct</span> <span class="token class-name">S</span> <span class="token punctuation">{</span>
<span class="token comment">// ...</span>
T t<span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre></div><p><code>this</code> is an rvalue, so it cannot be assigned to.</p> <h2 id="integer-literal"><a href="#integer-literal" class="header-anchor">#</a> Integer literal</h2> <p>An integer literal is a primary expression of the form</p> <ul><li>decimal-literal</li></ul> <p>It is a non-zero decimal digit (1, 2, 3, 4, 5, 6, 7, 8, 9), followed by zero or more decimal digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)</p> <p><code>int d = 42;</code></p> <ul><li>octal-literal</li></ul> <p>It is the digit zero (0) followed by zero or more octal digits (0, 1, 2, 3, 4, 5, 6, 7)</p> <p><code>int o = 052</code></p> <ul><li>hex-literal</li></ul> <p>It is the character sequence 0x or the character sequence 0X followed by one or more hexadecimal digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, A, b, B, c, C, d, D, e, E, f, F)</p> <p><code>int x = 0x2a;</code> <code>int X = 0X2A;</code></p> <ul><li>binary-literal (since C++14)</li></ul> <p>It is the character sequence 0b or the character sequence 0B followed by one or more binary digits (0, 1)</p> <p><code>int b = 0b101010; // C++14</code></p> <p>Integer-suffix, if provided, may contain one or both of the following (if both are provided, they may appear in any order:</p> <ul><li>unsigned-suffix (the character u or the character U)</li></ul> <p><code>unsigned int u_1 = 42u;</code></p> <ul><li>long-suffix (the character l or the character L) or the long-long-suffix (the character sequence ll or the character sequence LL) (since C++11)</li></ul> <p>The following variables are also initialized to the same value:</p> <div class="language-cpp extra-class"><pre class="language-cpp"><code><span class="token keyword">unsigned</span> <span class="token keyword">long</span> <span class="token keyword">long</span> l1 <span class="token operator">=</span> <span class="token number">18446744073709550592ull</span><span class="token punctuation">;</span> <span class="token comment">// C++11</span>
<span class="token keyword">unsigned</span> <span class="token keyword">long</span> <span class="token keyword">long</span> l2 <span class="token operator">=</span> <span class="token number">18'446'744'073'709'550'592llu</span><span class="token punctuation">;</span> <span class="token comment">// C++14</span>
<span class="token keyword">unsigned</span> <span class="token keyword">long</span> <span class="token keyword">long</span> l3 <span class="token operator">=</span> <span class="token number">1844'6744'0737'0955'0592uLL</span><span class="token punctuation">;</span> <span class="token comment">// C++14</span>
<span class="token keyword">unsigned</span> <span class="token keyword">long</span> <span class="token keyword">long</span> l4 <span class="token operator">=</span> <span class="token number">184467'440737'0'95505'92LLU</span><span class="token punctuation">;</span> <span class="token comment">// C++14</span>
</code></pre></div><p><strong>Notes</strong></p> <p>Letters in the integer literals are case-insensitive: 0xDeAdBaBeU and 0XdeadBABEu represent the same number (one exception is the long-long-suffix, which is either ll or LL, never lL or Ll)</p> <p>There are no negative integer literals. Expressions such as -1 apply the unary minus operator to the value represented by the literal, which may involve implicit type conversions.</p> <p>In C prior to C99 (but not in C++), unsuffixed decimal values that do not fit in long int are allowed to have the type unsigned long int.</p> <p>When used in a controlling expression of #if or #elif, all signed integer constants act as if they have type std::intmax_t and all unsigned integer constants act as if they have type std::uintmax_t.</p></div> <footer class="page-edit"><div class="edit-link"><a href="https://github.com/devtut/generate/edit/master/docs/cpp/literals.md" target="_blank" rel="noopener noreferrer">Edit this page on GitHub</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <!----></footer> <div class="page-nav"><p class="inner"><span class="prev">
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