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  26. <div class="titlepage"><div><div><h4 class="title">
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  27. <a name="phoenix.modules.statement.for_statement"></a><a class="link" href="for_statement.html" title="for_ Statement">for_ Statement</a>
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  28. </h4></div></div></div>
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  29. <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</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">&gt;</span>
    30. 

  30. </pre>
    31. 

  31. <p>
    32. 

  32.           The syntax is:
    33. 

  33.         </p>
    34. 

  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. 

  35. <span class="special">[</span>
    36. 

  36.     <span class="identifier">sequenced_statements</span>
    37. 

  37. <span class="special">]</span>
    38. 

  38. </pre>
    39. 

  39. <p>
    40. 

  40.           It is again very similar to the C++ for statement. Take note that the init_statement,
    41. 

  41.           conditional_expression and step_statement are separated by the comma instead of the semi-colon
    42. 

  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. 

  43.           <a class="link" href="../core/nothing.html" title="Nothing"><code class="computeroutput"><span class="identifier">nothing</span></code></a>
    44. 

  44.           actor can be useful.
    45. 

  45.         </p>
    46. 

  46. <p>
    47. 

  47.           Example: This code prints each element N times where N is the element's
    48. 

  48.           value. A newline terminates the printout of each value.
    49. 

  49.         </p>
    50. 

  50. <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">iii</span><span class="special">;</span>
    51. 

  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. 

  52.     <span class="special">(</span>
    53. 

  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">&lt;</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. 

  54.         <span class="special">[</span>
    55. 

  55.             <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">arg1</span> <span class="special">&lt;&lt;</span> <span class="string">", "</span>
    56. 

  56.         <span class="special">],</span>
    57. 

  57.         <span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">val</span><span class="special">(</span><span class="string">"\n"</span><span class="special">)</span>
    58. 

  58.     <span class="special">)</span>
    59. 

  59. <span class="special">);</span>
    60. 

  60. </pre>
    61. 

  61. <p>
    62. 

  62.           As before, all these are lazily evaluated. The result of such statements
    63. 

  63.           are in fact expressions that are passed on to STL's for_each function.
    64. 

  64.           In the viewpoint of <code class="computeroutput"><span class="identifier">for_each</span></code>,
    65. 

  65.           what was passed is just a functor, no more, no less.
    66. 

  66.         </p>
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  70. <td align="right"><div class="copyright-footer">Copyright &#169; 2002-2005, 2010 Joel de Guzman, Dan Marsden, Thomas Heller<p>
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  71.         Distributed under the Boost Software License, Version 1.0. (See accompanying
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  72.         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>)
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