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Node:<a name="Preprocessing">Preprocessing</a>,

Next:<a rel="next" accesskey="n" href="Whitespace.html#Whitespace">Whitespace</a>,

Up:<a rel="up" accesskey="u" href="Syntax.html#Syntax">Syntax</a>

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<h3 class="section">Preprocessing</h3>



   <p>The <code>as</code> internal preprocessor:

     <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.



     <li>removes all comments, replacing them with a single space, or an

appropriate number of newlines.



     <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 <small>GNU</small> C compiler driver

to get other "CPP" style preprocessing, by giving the input file a

<code>.S</code> suffix.  See <a href="../gcc.info/Overall-Options.html#Overall%20Options">Options Controlling the Kind of Output</a>.



   <p>Excess whitespace, comments, and character constants

cannot be used in the portions of the input text that are not

preprocessed.



   <p>If the first line of an input file is <code>#NO_APP</code> or if you use the

<code>-f</code> 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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