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| <title>Using as: Preprocessing</title> |
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| <a name="Preprocessing"></a> |
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| Next: <a href="Whitespace.html#Whitespace" accesskey="n" rel="next">Whitespace</a>, Up: <a href="Syntax.html#Syntax" accesskey="u" rel="up">Syntax</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Preprocessing-1"></a> |
| <h3 class="section">3.1 Preprocessing</h3> |
| |
| <a name="index-preprocessing"></a> |
| <p>The <code>as</code> internal preprocessor: |
| </p><ul> |
| <li> <a name="index-whitespace_002c-removed-by-preprocessor"></a> |
| adjusts and removes extra whitespace. It leaves one space or tab before |
| the keywords on a line, and turns any other whitespace on the line into |
| a single space. |
| |
| </li><li> <a name="index-comments_002c-removed-by-preprocessor"></a> |
| removes all comments, replacing them with a single space, or an |
| appropriate number of newlines. |
| |
| </li><li> <a name="index-constants_002c-converted-by-preprocessor"></a> |
| converts character constants into the appropriate numeric values. |
| </li></ul> |
| |
| <p>It does not do macro processing, include file handling, or |
| anything else you may get from your C compiler’s preprocessor. You can |
| do include file processing with the <code>.include</code> directive |
| (see <a href="Include.html#Include"><code>.include</code></a>). You can use the <small>GNU</small> C compiler driver |
| to get other “CPP” style preprocessing by giving the input file a |
| ‘<samp>.S</samp>’ suffix. See <a href="http://gcc.gnu.org/onlinedocs/gcc/Overall-Options.html#Overall-Options">Options Controlling the Kind of |
| Output</a> in <cite>Using GNU CC</cite>. |
| </p> |
| <p>Excess whitespace, comments, and character constants |
| cannot be used in the portions of the input text that are not |
| preprocessed. |
| </p> |
| <a name="index-turning-preprocessing-on-and-off"></a> |
| <a name="index-preprocessing_002c-turning-on-and-off"></a> |
| <a name="index-_0023NO_005fAPP"></a> |
| <a name="index-_0023APP"></a> |
| <p>If the first line of an input file is <code>#NO_APP</code> or if you use the |
| ‘<samp>-f</samp>’ option, whitespace and comments are not removed from the input file. |
| Within an input file, you can ask for whitespace and comment removal in |
| specific portions of the by putting a line that says <code>#APP</code> before the |
| text that may contain whitespace or comments, and putting a line that says |
| <code>#NO_APP</code> after this text. This feature is mainly intend to support |
| <code>asm</code> statements in compilers whose output is otherwise free of comments |
| and whitespace. |
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