ceph/src/boost/libs/preprocessor/doc/ref/line.html

   1 <html>
   2 <head>
   3         <title>BOOST_PP_LINE</title>
   4         <link rel="stylesheet" type="text/css" href="../styles.css">
   5 </head>
   6 <body>
   7         <div style="margin-left:  0px;">
   8                 The <b>BOOST_PP_LINE</b> macro places notes encoded as line directives in the preprocessing output.
   9         </div>
  10         <h4>Usage</h4>
  11                 <div class="code">
  12                         #line <b>BOOST_PP_LINE</b>(<i>line</i>, <i>file</i>)
  13                 </div>
  14         <h4>Arguments</h4>
  15                 <dl>
  16                         <dt>line</dt>
  17                         <dd>
  18                                 The new line number of the trailing line.&nbsp;
  19                                 The predefined macro <i>__LINE__</i> is commonly used.
  20                         </dd>
  21                         <dt>file</dt>
  22                         <dd>
  23                                 Typically the name of the current file.&nbsp;
  24                                 However, any informative text will work.&nbsp;
  25                                 This text is internally stringized, so quotation marks are unnecessary.
  26                         </dd>
  27                 </dl>
  28         <h4>Remarks</h4>
  29                 <div>
  30                         If the macro <b>BOOST_PP_CONFIG_EXTENDED_LINE_INFO</b> is defined as <i>1</i> and a <i>file-iteration</i>
  31                         is in progress, this macro will automatically insert debugging information about the state of <i>file-iteration</i>.&nbsp;
  32                         This information will show the all of the current iteration values with the inner most iteration last.
  33                 </div>
  34                 <div>
  35                         This information is useful when errors might be spanning multiple iterations of the same source text.&nbsp;
  36                         Finding any errors is sometimes less than straightforward.&nbsp;
  37                         Use of this macro can provide information to make this much easier.&nbsp;
  38                         For example, instead of getting several errors like this:
  39                         <div><i>
  40                                 "file.hpp", line 2: error: expected a ";"<br>
  41                                 "file.hpp", line 4: error: improperly terminated macro invocation<br>
  42                         </i></div>
  43                         You might get something like this instead....
  44                         <i><div>
  45                                 "file.hpp [1]", line 2: error: expected a ";"<br>
  46                                 "file.hpp [5]", line 4: error: improperly terminated macro invocation<br>
  47                         </i></div>
  48                         It is immediately evident that this error is spanning multiple iterations of the same source text.&nbsp;
  49                         If it wasn't, the same errors would occur on each iteration.
  50                 </div>
  51                 <div>
  52                         It must be noted however, that some compilers don't like filenames that aren't actually files.&nbsp;
  53                         Those compilers typically issues warnings about the bad filename.&nbsp;
  54                         This makes it a good idea to only define <b>BOOST_PP_CONFIG_EXTENDED_LINE_INFO</b> to <i>1</i> <i>only</i> when debugging.
  55                 </div>
  56         <h4>See Also</h4>
  57                 <ul>
  58                         <li><a href="config_extended_line_info.html">BOOST_PP_CONFIG_EXTENDED_LINE_INFO</a></li>
  59                 </ul>
  60         <h4>Requirements</h4>
  61                 <div>
  62                         <b>Header:</b> &nbsp;<a href="../headers/debug/line.html">&lt;boost/preprocessor/debug/line.hpp&gt;</a>
  63                 </div>
  64         <h4>Sample Code</h4>
  65 <div><pre>
  66 // sample.cpp
  67 #if !defined(<a href="is_iterating.html">BOOST_PP_IS_ITERATING</a>)
  68
  69    #define <a href="config_extended_line_info.html">BOOST_PP_CONFIG_EXTENDED_LINE_INFO</a> 1
  70
  71    #include &lt;<a href="../headers/arithmetic/dec.html">boost/preprocessor/arithmetic/dec.hpp</a>&gt;
  72    #include &lt;<a href="../headers/cat.html">boost/preprocessor/cat.hpp</a>&gt;
  73    #include &lt;<a href="../headers/debug/line.html">boost/preprocessor/debug/line.hpp</a>&gt;
  74    #include &lt;<a href="../headers/iteration/iterate.html">boost/preprocessor/iteration/iterate.hpp</a>&gt;
  75
  76    namespace sample {
  77
  78    #define <a href="iteration_params_x.html">BOOST_PP_ITERATION_PARAMS_1</a> (3, (1, 5, "sample.cpp"))
  79    #include <a href="iterate.html">BOOST_PP_ITERATE</a>()
  80
  81    } // sample
  82
  83    int main(void) {
  84       return 0;
  85    }
  86
  87 #else
  88
  89    #line <a href="line.html">BOOST_PP_LINE</a>(1, sample.cpp)
  90
  91    int <a href="cat.html">BOOST_PP_CAT</a>(x, <a href="iteration.html">BOOST_PP_ITERATION</a>())); // extra parenthesis
  92
  93    struct <a href="cat.html">BOOST_PP_CAT</a>(s, <a href="dec.html">BOOST_PP_DEC</a>(<a href="iteration.html">BOOST_PP_ITERATION</a>()) {
  94       // missing a parenthesis
  95       // ...
  96    };
  97
  98 #endif
  99 </pre></div>
 100         <hr size="1">
 101         <div style="margin-left: 0px;">
 102                 <i>© Copyright <a href="http://www.housemarque.com" target="_top">Housemarque Oy</a> 2002</i>
 103                 </br><i>© Copyright Paul Mensonides 2002</i>
 104         </div>
 105         <div style="margin-left: 0px;">
 106                 <p><small>Distributed under the Boost Software License, Version 1.0. (See
 107                 accompanying file <a href="../../../../LICENSE_1_0.txt">LICENSE_1_0.txt</a> or
 108                 copy at <a href=
 109                 "http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a>)</small></p>
 110         </div>
 111 </body>
 112 </html>