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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. |
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