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<a name="Preprocessing"></a>Next: <a rel="next" accesskey="n" href="Whitespace.html#Whitespace">Whitespace</a>,
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<h3 class="section">3.1 Preprocessing</h3>
<p><a name="index-preprocessing-114"></a>The <span class="command">as</span> internal preprocessor:
<a name="index-whitespace_002c-removed-by-preprocessor-115"></a>
<ul><li>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.
<p><a name="index-comments_002c-removed-by-preprocessor-116"></a><li>removes all comments, replacing them with a single space, or an
appropriate number of newlines.
<p><a name="index-constants_002c-converted-by-preprocessor-117"></a><li>converts character constants into the appropriate numeric values.
</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 <span class="sc">gnu</span> C compiler driver
to get other “CPP” style preprocessing by giving the input file a
<span class="samp">.S</span> suffix. See <a href="../gcc/Overall-Options.html#Overall-Options">Options Controlling the Kind of Output (Using GNU CC)</a>.
<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-118"></a><a name="index-preprocessing_002c-turning-on-and-off-119"></a><a name="index-_0023NO_005fAPP-120"></a><a name="index-_0023APP-121"></a>If the first line of an input file is <code>#NO_APP</code> or if you use the
<span class="samp">-f</span> 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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