1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>has_trivial_constructor</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. 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Note that using meta-programming 46 to omit a call to a single trivial-constructor call is of no benefit whatsoever. 47 However, if loops and/or exception handling code can also be omitted, then 48 some benefit in terms of code size and speed can be obtained. 49 </p> 50<p> 51 <span class="bold"><strong>Compiler Compatibility:</strong></span> Without some (as 52 yet unspecified) help from the compiler, has_trivial_constructor will never 53 report that a user-defined class or struct has a trivial constructor; this 54 is always safe, if possibly sub-optimal. In addition, in order to correctly 55 handle private or deleted default-constructors then C++11's <code class="computeroutput"><span class="identifier">deltype</span></code> is required. Currently (May 2015) 56 compilers more recent than Visual C++ 8, GCC-4.3, Greenhills 6.0, Intel-11.0, 57 and Codegear have the necessary compiler <a class="link" href="../intrinsics.html" title="Support for Compiler Intrinsics">intrinsics</a> 58 to ensure that this trait "just works". You may also test to see 59 if the necessary <a class="link" href="../intrinsics.html" title="Support for Compiler Intrinsics">intrinsics</a> 60 are available by checking to see if the macro <code class="computeroutput"><span class="identifier">BOOST_HAS_TRIVIAL_CONSTRUCTOR</span></code> 61 is defined. 62 </p> 63<p> 64 <span class="bold"><strong>C++ Standard Reference:</strong></span> 12.1p6. 65 </p> 66<p> 67 <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span> 68 <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">has_trivial_constructor</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 69 or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 70 </p> 71<p> 72 <span class="bold"><strong>Examples:</strong></span> 73 </p> 74<div class="blockquote"><blockquote class="blockquote"><p> 75 <code class="computeroutput"><span class="identifier">has_trivial_constructor</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code> inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. 76 </p></blockquote></div> 77<div class="blockquote"><blockquote class="blockquote"><p> 78 <code class="computeroutput"><span class="identifier">has_trivial_constructor</span><span class="special"><</span><span class="keyword">char</span><span class="special">*>::</span><span class="identifier">type</span></code> 79 is the type <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. 80 </p></blockquote></div> 81<div class="blockquote"><blockquote class="blockquote"><p> 82 <code class="computeroutput"><span class="identifier">has_trivial_constructor</span><span class="special"><</span><span class="keyword">int</span> <span class="special">(*)(</span><span class="keyword">long</span><span class="special">)>::</span><span class="identifier">value</span></code> 83 is an integral constant expression that evaluates to <span class="emphasis"><em>true</em></span>. 84 </p></blockquote></div> 85<div class="blockquote"><blockquote class="blockquote"><p> 86 <code class="computeroutput"><span class="identifier">has_trivial_constructor</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">>::</span><span class="identifier">value</span></code> 87 is an integral constant expression that evaluates to <span class="emphasis"><em>false</em></span>. 88 </p></blockquote></div> 89<div class="blockquote"><blockquote class="blockquote"><p> 90 <code class="computeroutput"><span class="identifier">has_trivial_constructor</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_type</span></code> 91 is the type <code class="computeroutput"><span class="keyword">bool</span></code>. 92 </p></blockquote></div> 93</div> 94<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 95<td align="left"></td> 96<td align="right"><div class="copyright-footer">Copyright © 2000, 2011 Adobe Systems Inc, David Abrahams, 97 Frederic Bron, Steve Cleary, Beman Dawes, Glen Fernandes, Aleksey Gurtovoy, 98 Howard Hinnant, Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander 99 Nasonov, Thorsten Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert 100 Stewart and Steven Watanabe<p> 101 Distributed under the Boost Software License, Version 1.0. (See accompanying 102 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 103 </p> 104</div></td> 105</tr></table> 106<hr> 107<div class="spirit-nav"> 108<a accesskey="p" href="has_trivial_assign.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.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="has_trivial_copy.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 109</div> 110</body> 111</html> 112
