1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>for_ 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="___do_while_____statement.html" title="do_while_ Statement"> 10<link rel="next" href="try__catch__statement.html" title="try_ catch_ 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="___do_while_____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="try__catch__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.for_statement"></a><a class="link" href="for_statement.html" title="for_ Statement">for_ 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">for</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">for_</span><span class="special">(</span><span class="identifier">init_statement</span><span class="special">,</span> <span class="identifier">conditional_expression</span><span class="special">,</span> <span class="identifier">step_statement</span><span class="special">)</span> 35<span class="special">[</span> 36 <span class="identifier">sequenced_statements</span> 37<span class="special">]</span> 38</pre> 39<p> 40 It is again very similar to the C++ for statement. Take note that the init_statement, 41 conditional_expression and step_statement are separated by the comma instead of the semi-colon 42 and each must be present (i.e. <code class="computeroutput"><span class="identifier">for_</span><span class="special">(,,)</span></code> is invalid). This is a case where the 43 <a class="link" href="../core/nothing.html" title="Nothing"><code class="computeroutput"><span class="identifier">nothing</span></code></a> 44 actor can be useful. 45 </p> 46<p> 47 Example: This code prints each element N times where N is the element's 48 value. A newline terminates the printout of each value. 49 </p> 50<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">iii</span><span class="special">;</span> 51<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> 52 <span class="special">(</span> 53 <span class="identifier">for_</span><span class="special">(</span><span class="identifier">ref</span><span class="special">(</span><span class="identifier">iii</span><span class="special">)</span> <span class="special">=</span> <span class="number">0</span><span class="special">,</span> <span class="identifier">ref</span><span class="special">(</span><span class="identifier">iii</span><span class="special">)</span> <span class="special"><</span> <span class="identifier">arg1</span><span class="special">,</span> <span class="special">++</span><span class="identifier">ref</span><span class="special">(</span><span class="identifier">iii</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">", "</span> 56 <span class="special">],</span> 57 <span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">val</span><span class="special">(</span><span class="string">"\n"</span><span class="special">)</span> 58 <span class="special">)</span> 59<span class="special">);</span> 60</pre> 61<p> 62 As before, all these are lazily evaluated. The result of such statements 63 are in fact expressions that are passed on to STL's for_each function. 64 In the viewpoint of <code class="computeroutput"><span class="identifier">for_each</span></code>, 65 what was passed is just a functor, no more, no less. 66 </p> 67</div> 68<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 69<td align="left"></td> 70<td align="right"><div class="copyright-footer">Copyright © 2002-2005, 2010, 2014, 2015 Joel de Guzman, Dan Marsden, Thomas 71 Heller, John Fletcher<p> 72 Distributed under the Boost Software License, Version 1.0. (See accompanying 73 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>) 74 </p> 75</div></td> 76</tr></table> 77<hr> 78<div class="spirit-nav"> 79<a accesskey="p" href="___do_while_____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="try__catch__statement.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 80</div> 81</body> 82</html> 83
