1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>if_else_ Statement</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. Phoenix 3.2.0"> 8<link rel="up" href="../statement.html" title="Statement"> 9<link rel="prev" href="if__statement.html" title="if_ Statement"> 10<link rel="next" href="switch__statement.html" title="switch_ Statement"> 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="if__statement.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../statement.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="switch__statement.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h4 class="title"> 27<a name="phoenix.modules.statement.___if_else_____statement"></a><a class="link" href="___if_else_____statement.html" title="if_else_ Statement">if_else_ Statement</a> 28</h4></div></div></div> 29<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">phoenix</span><span class="special">/</span><span class="identifier">statement</span><span class="special">/</span><span class="keyword">if</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 30</pre> 31<p> 32 The syntax is 33 </p> 34<pre class="programlisting"><span class="identifier">if_</span><span class="special">(</span><span class="identifier">conditional_expression</span><span class="special">)</span> 35<span class="special">[</span> 36 <span class="identifier">sequenced_statements</span> 37<span class="special">]</span> 38<span class="special">.</span><span class="identifier">else_</span> 39<span class="special">[</span> 40 <span class="identifier">sequenced_statements</span> 41<span class="special">]</span> 42</pre> 43<p> 44 Take note that <code class="computeroutput"><span class="keyword">else</span></code> has a 45 leading dot and a trailing underscore: <code class="computeroutput"><span class="special">.</span><span class="identifier">else_</span></code> 46 </p> 47<p> 48 Example: This code prints out all the elements and appends <code class="computeroutput"><span class="string">" > 5"</span></code>, <code class="computeroutput"><span class="string">" 49 == 5"</span></code> or <code class="computeroutput"><span class="string">" < 5"</span></code> 50 depending on the element's actual value: 51 </p> 52<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span><span class="special">(</span><span class="identifier">c</span><span class="special">.</span><span class="identifier">begin</span><span class="special">(),</span> <span class="identifier">c</span><span class="special">.</span><span class="identifier">end</span><span class="special">(),</span> 53 <span class="identifier">if_</span><span class="special">(</span><span class="identifier">arg1</span> <span class="special">></span> <span class="number">5</span><span class="special">)</span> 54 <span class="special">[</span> 55 <span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">arg1</span> <span class="special"><<</span> <span class="string">" > 5\n"</span> 56 <span class="special">]</span> 57 <span class="special">.</span><span class="identifier">else_</span> 58 <span class="special">[</span> 59 <span class="identifier">if_</span><span class="special">(</span><span class="identifier">arg1</span> <span class="special">==</span> <span class="number">5</span><span class="special">)</span> 60 <span class="special">[</span> 61 <span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">arg1</span> <span class="special"><<</span> <span class="string">" == 5\n"</span> 62 <span class="special">]</span> 63 <span class="special">.</span><span class="identifier">else_</span> 64 <span class="special">[</span> 65 <span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">arg1</span> <span class="special"><<</span> <span class="string">" < 5\n"</span> 66 <span class="special">]</span> 67 <span class="special">]</span> 68<span class="special">);</span> 69</pre> 70<p> 71 Notice how the <code class="computeroutput"><span class="identifier">if_else_</span></code> 72 statement is nested. 73 </p> 74</div> 75<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 76<td align="left"></td> 77<td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2010, 2014, 2015 Joel de Guzman, Dan Marsden, Thomas 78 Heller, John Fletcher<p> 79 Distributed under the Boost Software License, Version 1.0. (See accompanying 80 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>) 81 </p> 82</div></td> 83</tr></table> 84<hr> 85<div class="spirit-nav"> 86<a accesskey="p" href="if__statement.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../statement.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="switch__statement.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 87</div> 88</body> 89</html> 90
