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<h3 class="section">10.3 Traditional miscellany</h3>
<p>Here are some things to be aware of when using the traditional
preprocessor.
<ul>
<li>Preprocessing directives are recognized only when their leading
‘<samp><span class="samp">#</span></samp>’ appears in the first column. There can be no whitespace
between the beginning of the line and the ‘<samp><span class="samp">#</span></samp>’, but whitespace can
follow the ‘<samp><span class="samp">#</span></samp>’.
<li>A true traditional C preprocessor does not recognize ‘<samp><span class="samp">#error</span></samp>’ or
‘<samp><span class="samp">#pragma</span></samp>’, and may not recognize ‘<samp><span class="samp">#elif</span></samp>’. CPP supports all
the directives in traditional mode that it supports in ISO mode,
including extensions, with the exception that the effects of
‘<samp><span class="samp">#pragma GCC poison</span></samp>’ are undefined.
<li>__STDC__ is not defined.
<li>If you use digraphs the behavior is undefined.
<li>If a line that looks like a directive appears within macro arguments,
the behavior is undefined.
</ul>
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