1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>explicit_operator_bool</title> 5<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Chapter 1. Boost.Core"> 8<link rel="up" href="../index.html" title="Chapter 1. Boost.Core"> 9<link rel="prev" href="exchange.html" title="exchange"> 10<link rel="next" href="first_scalar.html" title="first_scalar"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="exchange.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="first_scalar.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 27<a name="core.explicit_operator_bool"></a><a class="link" href="explicit_operator_bool.html" title="explicit_operator_bool">explicit_operator_bool</a> 28</h2></div></div></div> 29<div class="toc"><dl class="toc"> 30<dt><span class="section"><a href="explicit_operator_bool.html#core.explicit_operator_bool.overview">Overview</a></span></dt> 31<dt><span class="section"><a href="explicit_operator_bool.html#core.explicit_operator_bool.examples">Examples</a></span></dt> 32<dt><span class="section"><a href="explicit_operator_bool.html#core.explicit_operator_bool.history">History</a></span></dt> 33</dl></div> 34<div class="simplesect"> 35<div class="titlepage"><div><div><h3 class="title"> 36<a name="idm45312828509824"></a>Authors</h3></div></div></div> 37<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 38 Andrey Semashev 39 </li></ul></div> 40</div> 41<div class="section"> 42<div class="titlepage"><div><div><h3 class="title"> 43<a name="core.explicit_operator_bool.overview"></a><a class="link" href="explicit_operator_bool.html#core.explicit_operator_bool.overview" title="Overview">Overview</a> 44</h3></div></div></div> 45<p> 46 Header <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">core</span><span class="special">/</span><span class="identifier">explicit_operator_bool</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 47 provides <code class="computeroutput"><span class="identifier">BOOST_EXPLICIT_OPERATOR_BOOL</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL</span><span class="special">()</span></code> compatibility helper macros that expand 48 to an explicit conversion operator to <code class="computeroutput"><span class="keyword">bool</span></code>. 49 For compilers not supporting explicit conversion operators introduced in 50 C++11 the macros expand to a conversion operator that implements the <a href="http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Safe_bool" target="_top">safe bool 51 idiom</a>. In case if the compiler is not able to handle safe bool idiom 52 well the macros expand to a regular conversion operator to <code class="computeroutput"><span class="keyword">bool</span></code>. 53 </p> 54</div> 55<div class="section"> 56<div class="titlepage"><div><div><h3 class="title"> 57<a name="core.explicit_operator_bool.examples"></a><a class="link" href="explicit_operator_bool.html#core.explicit_operator_bool.examples" title="Examples">Examples</a> 58</h3></div></div></div> 59<p> 60 Both macros are intended to be placed within a user's class definition. The 61 generated conversion operators will be implemented in terms of <code class="computeroutput"><span class="keyword">operator</span><span class="special">!()</span></code> 62 that should be defined by user in this class. In case of <code class="computeroutput"><span class="identifier">BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL</span><span class="special">()</span></code> the generated conversion operator will 63 be declared <code class="computeroutput"><span class="keyword">constexpr</span></code> which 64 requires the corresponding <code class="computeroutput"><span class="keyword">operator</span><span class="special">!()</span></code> to also be <code class="computeroutput"><span class="keyword">constexpr</span></code>. 65 </p> 66<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <span class="identifier">T</span> <span class="special">></span> 67<span class="keyword">class</span> <span class="identifier">my_ptr</span> 68<span class="special">{</span> 69 <span class="identifier">T</span><span class="special">*</span> <span class="identifier">m_p</span><span class="special">;</span> 70 71<span class="keyword">public</span><span class="special">:</span> 72 <span class="identifier">BOOST_EXPLICIT_OPERATOR_BOOL</span><span class="special">()</span> 73 74 <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span> 75 <span class="special">{</span> 76 <span class="keyword">return</span> <span class="special">!</span><span class="identifier">m_p</span><span class="special">;</span> 77 <span class="special">}</span> 78<span class="special">};</span> 79</pre> 80<p> 81 Now <code class="computeroutput"><span class="identifier">my_ptr</span></code> can be used in 82 conditional expressions, similarly to a regular pointer: 83 </p> 84<pre class="programlisting"><span class="identifier">my_ptr</span><span class="special"><</span> <span class="keyword">int</span> <span class="special">></span> <span class="identifier">p</span><span class="special">;</span> 85<span class="keyword">if</span> <span class="special">(</span><span class="identifier">p</span><span class="special">)</span> 86 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"true"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 87</pre> 88</div> 89<div class="section"> 90<div class="titlepage"><div><div><h3 class="title"> 91<a name="core.explicit_operator_bool.history"></a><a class="link" href="explicit_operator_bool.html#core.explicit_operator_bool.history" title="History">History</a> 92</h3></div></div></div> 93<h5> 94<a name="core.explicit_operator_bool.history.h0"></a> 95 <span class="phrase"><a name="core.explicit_operator_bool.history.boost_1_56"></a></span><a class="link" href="explicit_operator_bool.html#core.explicit_operator_bool.history.boost_1_56">boost 96 1.56</a> 97 </h5> 98<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 99<li class="listitem"> 100 Added new macros <code class="computeroutput"><span class="identifier">BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT</span></code> 101 and <code class="computeroutput"><span class="identifier">BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL</span></code> 102 to define <code class="computeroutput"><span class="keyword">noexcept</span></code> and 103 <code class="computeroutput"><span class="keyword">constexpr</span></code> operators. 104 </li> 105<li class="listitem"> 106 The header moved to Boost.Core. 107 </li> 108</ul></div> 109<h5> 110<a name="core.explicit_operator_bool.history.h1"></a> 111 <span class="phrase"><a name="core.explicit_operator_bool.history.boost_1_55"></a></span><a class="link" href="explicit_operator_bool.html#core.explicit_operator_bool.history.boost_1_55">boost 112 1.55</a> 113 </h5> 114<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 115 The macro was extracted from Boost.Log. 116 </li></ul></div> 117</div> 118</div> 119<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 120<td align="left"></td> 121<td align="right"><div class="copyright-footer">Copyright © 2014 Peter Dimov<br>Copyright © 2014 Glen Fernandes<br>Copyright © 2014 Andrey Semashev<p> 122 Distributed under the <a href="http://boost.org/LICENSE_1_0.txt" target="_top">Boost 123 Software License, Version 1.0</a>. 124 </p> 125</div></td> 126</tr></table> 127<hr> 128<div class="spirit-nav"> 129<a accesskey="p" href="exchange.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="first_scalar.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 130</div> 131</body> 132</html> 133
