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104 lines
3.5 KiB
HTML
104 lines
3.5 KiB
HTML
<html>
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<head>
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<title>BOOST_PP_LINE</title>
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<link rel="stylesheet" type="text/css" href="../styles.css">
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<script language="javascript" type="text/javascript" src="../scripts.js"></script>
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</head>
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<body onload="init('sample');">
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<div style="margin-left: 0px;">
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The <b>BOOST_PP_LINE</b> macro places notes encoded as line directives in the preprocessing output.
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</div>
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<h4>Usage</h4>
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<div class="code">
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#line <b>BOOST_PP_LINE</b>(<i>line</i>, <i>file</i>)
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</div>
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<h4>Arguments</h4>
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<dl>
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<dt>line</dt>
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<dd>
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The new line number of the trailing line.
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The predefined macro <i>__LINE__</i> is commonly used.
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</dd>
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<dt>file</dt>
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<dd>
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Typically the name of the current file.
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However, any informative text will work.
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This text is internally stringized, so quotation marks are unnecessary.
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</dd>
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</dl>
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<h4>Remarks</h4>
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<div>
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If the macro <b>BOOST_PP_CONFIG_EXTENDED_LINE_INFO</b> is defined as <i>1</i> and a <i>file-iteration</i>
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is in progress, this macro will automatically insert debugging information about the state of <i>file-iteration</i>.
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This information will show the all of the current iteration values with the inner most iteration last.
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</div>
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<div>
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This information is useful when errors might be spanning multiple iterations of the same source text.
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Finding any errors is sometimes less than straightforward.
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Use of this macro can provide information to make this much easier.
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For example, instead of getting several errors like this:
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<div><i>
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"file.hpp", line 2: error: expected a ";"<br>
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"file.hpp", line 4: error: improperly terminated macro invocation<br>
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</i></div>
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You might get something like this instead....
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<i><div>
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"file.hpp [1]", line 2: error: expected a ";"<br>
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"file.hpp [5]", line 4: error: improperly terminated macro invocation<br>
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</i></div>
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It is immediately evident that this error is spanning multiple iterations of the same source text.
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If it wasn't, the same errors would occur on each iteration.
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</div>
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<div>
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It must be noted however, that some compilers don't like filenames that aren't actually files.
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Those compilers typically issues warnings about the bad filename.
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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.
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</div>
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<h4>See Also</h4>
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<ul>
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<li><a href="config_extended_line_info.html">BOOST_PP_CONFIG_EXTENDED_LINE_INFO</a></li>
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</ul>
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<h4>Requirements</h4>
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<div>
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<b>Header:</b> <a href="../headers/debug/line.hpp.html"><boost/preprocessor/debug/line.hpp></a>
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</div>
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<h4><a class="local" onclick="toggle('sample');" onmouseover="change(this);" onmouseout="revert(this);">Sample Code</a></h4>
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<div id="sample"><pre>
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// sample.cpp
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#if !defined(BOOST_PP_IS_ITERATING)
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#define BOOST_PP_CONFIG_EXTENDED_LINE_INFO 1
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#include <boost/preprocessor/arithmetic/dec.hpp>
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#include <boost/preprocessor/cat.hpp>
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#include <boost/preprocessor/debug/line.hpp>
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#include <boost/preprocessor/iteration/iterate.hpp>
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namespace sample {
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#define BOOST_PP_ITERATION_PARAMS_1 (3, (1, 5, "sample.cpp"))
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#include BOOST_PP_ITERATE()
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} // sample
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int main(void) {
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return 0;
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}
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#else
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#line BOOST_PP_LINE(1, sample.cpp)
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int BOOST_PP_CAT(x, BOOST_PP_ITERATION())); // extra parenthesis
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struct BOOST_PP_CAT(s, BOOST_PP_DEC(BOOST_PP_ITERATION()) {
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// missing a parenthesis
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// ...
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};
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#endif
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<pre></div>
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</body>
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</html>
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