preprocessor/doc/reference/cat_8hpp.html

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<hr><h1>cat.hpp File Reference</h1><a href="../../../../boost/preprocessor/cat.hpp">Click here to see the header.</a>. 
<a href="#_details">More...</a>
<p>
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<tr><td colspan=2><br><h2>Defines</h2></td></tr>
<tr><td nowrap align=right valign=top>#define&nbsp;</td><td valign=bottom><a class="el" href="cat_8hpp.html#a0">BOOST_PP_CAT</a>(X, Y)</td></tr>
<tr><td>&nbsp;</td><td><font size=-1><em>Delays the catenation of X and Y.</em> <a href="#a0">More...</a><em></em></font><br><br></td></tr>
<tr><td nowrap align=right valign=top>#define&nbsp;</td><td valign=bottom><a class="el" href="cat_8hpp.html#a1">BOOST_PREPROCESSOR_CAT</a>(X, Y)</td></tr>
<tr><td>&nbsp;</td><td><font size=-1><em>Obsolete.</em> <a href="#a1">More...</a><em></em></font><br><br></td></tr>
</table>
<hr><a name="_details"></a><h2>Detailed Description</h2>
<a href="../../../../boost/preprocessor/cat.hpp">Click here to see the header.</a>.
<p>

<p>
<hr><h2>Define Documentation</h2>
<a name="a0" doxytag="cat.hpp::BOOST_PP_CAT"></a><p>
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          <td class="md" nowrap valign="top"> #define BOOST_PP_CAT</td>
          <td class="md" valign="top">(&nbsp;</td>
          <td class="md" nowrap valign="top">X,         <tr>
          <td></td>
          <td></td>
          <td class="md" nowrap>Y&nbsp;</td>
          <td class="mdname1" valign="top" nowrap>&nbsp;          </td>
          <td class="md" valign="top">)&nbsp;</td>
          <td class="md" nowrap>
      </table>
    </td>
  </tr>
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<table cellspacing=5 cellpadding=0 border=0>
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    <td>
      &nbsp;
    </td>
    <td>

<p>
Delays the catenation of X and Y.
<p>
For example,
<p>
<pre><div class="fragment"><pre>
  #define STATIC_ASSERT(EXPR)\
    enum\
    { BOOST_PP_CAT(static_check_,__LINE__) = (EXPR) ? 1 : -1\
    };\
    typedef char\
      BOOST_PP_CAT(static_assert_,__LINE__)\
      [ BOOST_PP_CAT(static_check_,__LINE__)\
      ]

  // ...

  STATIC_ASSERT(sizeof(int) &lt;= sizeof(long));
</pre></div></pre>
<p>
expands to:
<p>
<pre><div class="fragment"><pre>
  enum
  { static_check_152 = (sizeof(int) &lt;= sizeof(long)) ? 1 : -1
  };
  typedef char
    static_assert_152
    [ static_check_152
    ];
</pre></div></pre>
<p>
Using <a class="el" href="cat_8hpp.html#a0">BOOST_PP_CAT</a>() above lets the PP expand the __LINE__. If the above code would use the ## operator directly then __LINE__ would not be expanded and the above would expand to:
<p>
<pre><div class="fragment"><pre>
  enum
  { static_check___LINE__ = (sizeof(int) &lt;= sizeof(long)) ? 1 : -1
  };
  typedef char
    static_assert___LINE__
    [ static_check___LINE__
    ];
</pre></div></pre>     </td>
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<a name="a1" doxytag="cat.hpp::BOOST_PREPROCESSOR_CAT"></a><p>
<table width="100%" cellpadding="2" cellspacing="0" border="0">
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          <td class="md" nowrap valign="top"> #define BOOST_PREPROCESSOR_CAT</td>
          <td class="md" valign="top">(&nbsp;</td>
          <td class="md" nowrap valign="top">X,         <tr>
          <td></td>
          <td></td>
          <td class="md" nowrap>Y&nbsp;</td>
          <td class="mdname1" valign="top" nowrap>&nbsp;          </td>
          <td class="md" valign="top">)&nbsp;</td>
          <td class="md" nowrap>
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    </td>
  </tr>
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<table cellspacing=5 cellpadding=0 border=0>
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    <td>
      &nbsp;
    </td>
    <td>

<p>
Obsolete.
<p>
Use <a class="el" href="cat_8hpp.html#a0">BOOST_PP_CAT</a>().     </td>
  </tr>
</table>
<hr>
<p><EFBFBD> Copyright Housemarque Oy 2001</p>
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