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129 lines
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129 lines
6.9 KiB
HTML
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<title>Supported Pragma Directives</title>
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<td width="21"> <h1></h1></td>
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<td width="885"> <font face="Verdana, Arial, Helvetica, sans-serif"><b><font size="6">Supported
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Pragma Directives</font></b></font></td>
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<p>The Wave preprocessor library supports a couple of specific <tt>#pragma</tt>
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directives, which may be used to control some of the library features. All directives
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described here are usable as conventional <tt>#pragma</tt> directives and as
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<tt>operator _Pragma</tt> (if variadics are enabled). So for instance the
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following directives are functionally identical:</p>
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<pre> #pragma wave trace(enable) </pre>
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<p>and </p>
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<pre> _Pragma("wave trace(enable)")</pre>
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<p>All <tt>Wave</tt> specific pragma's must have the general form <tt>'wave option[(value)]'</tt>,
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where <tt>'wave'</tt> is the specific keyword, <tt>'option'</tt> is the concrete
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pragma functionality to trigger and <tt>'value'</tt> is an optional value to
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be supplied to the <tt>'option'</tt> functionality. The following table lists
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all possible pragma functions supported by the <tt>Wave</tt> library. </p>
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<table width="77%" border="0" align="center">
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<tr>
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<td colspan="4"> <p class="table_title">Supported pragma's</p></td>
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</tr>
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<tr>
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<td> <p class="toc_title" width="36%">pragma option</p></td>
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<td> <p class="toc_title" width="28%">pragma value</p></td>
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<td> <p class="toc_title" width="36%">description</p></td>
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<td> <p class="toc_title" width="36%">supported by</p></td>
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</tr>
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<tr>
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<td class="table_cells" width="19%"> <p>trace</p></td>
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<td class="table_cells" width="18%"> <p>enable/on/1<br>
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disable/off/0</p></td>
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<td class="table_cells" width="43%"><p>Enable or disable the tracing of the
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macro expansion process. This is needed, even if there is given the --trace
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command line option, because the trace output is generated only, if there
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is at least one trace(enable) pragma found.</p></td>
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<td class="table_cells" width="20%"><p>Wave library</p></td>
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</tr>
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<tr>
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<td class="table_cells"><p>stop</p></td>
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<td class="table_cells"><p>message</p></td>
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<td class="table_cells"><p>Stop the execution of <tt>Wave</tt> and print out
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the given message. This is very helpful for direct debugging purposes.</p></td>
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<td class="table_cells"><p>Wave library</p></td>
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</tr>
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<tr>
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<td class="table_cells"><p>system</p></td>
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<td class="table_cells"><p>command</p></td>
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<td class="table_cells"><p>Try to spawn the 'command' as a new operating system
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command and intercept the generated stdout and stderr. The stdout output
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of this command (if any) is retokenized and used as the replacement text
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for the whole pragma, the stderr output is ignored. The command is considered
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to be successful, if/when the return value is zero, otherwise an error
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is reported. <br>
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</p></td>
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<td class="table_cells"><p>Wave library</p></td>
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</tr>
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<tr>
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<td class="table_cells"><p>timer</p></td>
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<td class="table_cells"><p> restart/0<br>
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<no value> <br>
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suspend<br>
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resume </p></td>
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<td class="table_cells"><p>The value <tt>restart</tt> set the current elapsed
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time to 0 and restarts the timer.<br>
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If no value is provided, the current elpsed time is printed to the std::cerr
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stream.<br>
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The values <tt>suspend</tt> and <tt>resume</tt> allow to temporarily stop
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the timing.</p></td>
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<td class="table_cells"><p>Wave driver</p></td>
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</tr>
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</table>
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<p>All pragma's not listed here but flagged as <tt>'wave'</tt> are reported as
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errors. The handling of all remaining pragma's depends on the compilation constant
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<code><tt>WAVE_RETURN_PRAGMA_DIRECTIVES</tt></code>, which allows to specify,
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if those pragmas are left unchanged in the output stream or not. Please note,
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that the operator _Pragma variant is always subject to full preprocessing, before
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the pragma itself is evaluated. The #pragma variant is subject to preprocessing
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only, if the <code><tt>WAVE_PREPROCESS_PRAGMA_BODY</tt></code> compilation constant
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was specified during compilation. For more information about the possible compilation
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constants look <a href="compiletime_config.html">here</a>.</p>
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<p>Additionally the Wave preprocessor supports the <tt>#pragma once</tt> directive,
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which specifies that the file, in which the pragma resides, will be included
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(opened) only once by the compiler in a build. This may be used to optimize
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the preprocessing of larger compilation units, which include a lot of files. Note though, that the #pragma once directive is supported only, if the compile time constant <tt>WAVE_SUPPORT_PRAGMA_ONCE</tt> was given during compilation of the library</span>.</p>
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<p>It is fairly easy to implement your own <tt>#pragma wave ... </tt> directives. All you have to do is to implement your own <tt>interpret_pragma</tt> function (see <a href="class_reference_tracepolicy.html#interpret_pragma">here</a>) which should the handle additional directives. For an example of how to do it, you may have a look at the Wave driver application, which implements the <tt>#pragma wave timer()</tt> directive with the help of a supplied <tt>interpret_pragma</tt> function. </p>
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<table border="0">
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<tr>
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<td width="10"></td>
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<td width="30"><a href="./index.html"><img src="theme/u_arr.gif" border="0"></a></td>
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<td width="30"><a href="predefined_macros.html"><img src="theme/l_arr.gif" border="0"></a></td>
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<td width="30"><a href="macro_expansion_process.html"><img src="theme/r_arr.gif" border="0"></a></td>
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</tr>
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</table>
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<hr size="1">
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<p class="copyright">Copyright © 2003-2004 Hartmut Kaiser<br>
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<br>
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<font size="2">Use, modification and distribution is subject to the Boost Software
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License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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</font> </p>
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<span class="updated">Last updated:
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<!-- #BeginDate format:fcAm1m -->Wednesday, January 14, 2004 12:48<!-- #EndDate -->
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</span>
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<p> </p>
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