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<title>Using as: Preprocessing</title>

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<a name="Preprocessing"></a>
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<p>
Next: <a href="Whitespace.html#Whitespace" accesskey="n" rel="next">Whitespace</a>, Up: <a href="Syntax.html#Syntax" accesskey="u" rel="up">Syntax</a> &nbsp; [<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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<hr>
<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&rsquo;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 &ldquo;CPP&rdquo; style preprocessing by giving the input file a
&lsquo;<samp>.S</samp>&rsquo; suffix.  See <a href="../gcc info/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
&lsquo;<samp>-f</samp>&rsquo; 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.
</p>


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