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| 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> | |
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| 80 | </div> | |
| 81 | </body> | |
| 82 | </html> |