1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- This file documents the GNU Assembler "as". 4 5Copyright (C) 1991-2021 Free Software Foundation, Inc. 6 7Permission is granted to copy, distribute and/or modify this document 8under the terms of the GNU Free Documentation License, Version 1.3 9or any later version published by the Free Software Foundation; 10with no Invariant Sections, with no Front-Cover Texts, and with no 11Back-Cover Texts. A copy of the license is included in the 12section entitled "GNU Free Documentation License". 13 --> 14<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> 15<head> 16<title>Using as: Preprocessing</title> 17 18<meta name="description" content="Using as: Preprocessing"> 19<meta name="keywords" content="Using as: Preprocessing"> 20<meta name="resource-type" content="document"> 21<meta name="distribution" content="global"> 22<meta name="Generator" content="makeinfo"> 23<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 24<link href="index.html#Top" rel="start" title="Top"> 25<link href="AS-Index.html#AS-Index" rel="index" title="AS Index"> 26<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> 27<link href="Syntax.html#Syntax" rel="up" title="Syntax"> 28<link href="Whitespace.html#Whitespace" rel="next" title="Whitespace"> 29<link href="Syntax.html#Syntax" rel="previous" title="Syntax"> 30<style type="text/css"> 31<!-- 32a.summary-letter {text-decoration: none} 33blockquote.smallquotation {font-size: smaller} 34div.display {margin-left: 3.2em} 35div.example {margin-left: 3.2em} 36div.indentedblock {margin-left: 3.2em} 37div.lisp {margin-left: 3.2em} 38div.smalldisplay {margin-left: 3.2em} 39div.smallexample {margin-left: 3.2em} 40div.smallindentedblock {margin-left: 3.2em; font-size: smaller} 41div.smalllisp {margin-left: 3.2em} 42kbd {font-style:oblique} 43pre.display {font-family: inherit} 44pre.format {font-family: inherit} 45pre.menu-comment {font-family: serif} 46pre.menu-preformatted {font-family: serif} 47pre.smalldisplay {font-family: inherit; font-size: smaller} 48pre.smallexample {font-size: smaller} 49pre.smallformat {font-family: inherit; font-size: smaller} 50pre.smalllisp {font-size: smaller} 51span.nocodebreak {white-space:nowrap} 52span.nolinebreak {white-space:nowrap} 53span.roman {font-family:serif; font-weight:normal} 54span.sansserif {font-family:sans-serif; font-weight:normal} 55ul.no-bullet {list-style: none} 56--> 57</style> 58 59 60</head> 61 62<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> 63<a name="Preprocessing"></a> 64<div class="header"> 65<p> 66Next: <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> 67</div> 68<hr> 69<a name="Preprocessing-1"></a> 70<h3 class="section">3.1 Preprocessing</h3> 71 72<a name="index-preprocessing"></a> 73<p>The <code>as</code> internal preprocessor: 74</p><ul> 75<li> <a name="index-whitespace_002c-removed-by-preprocessor"></a> 76adjusts and removes extra whitespace. It leaves one space or tab before 77the keywords on a line, and turns any other whitespace on the line into 78a single space. 79 80</li><li> <a name="index-comments_002c-removed-by-preprocessor"></a> 81removes all comments, replacing them with a single space, or an 82appropriate number of newlines. 83 84</li><li> <a name="index-constants_002c-converted-by-preprocessor"></a> 85converts character constants into the appropriate numeric values. 86</li></ul> 87 88<p>It does not do macro processing, include file handling, or 89anything else you may get from your C compiler’s preprocessor. You can 90do include file processing with the <code>.include</code> directive 91(see <a href="Include.html#Include"><code>.include</code></a>). You can use the <small>GNU</small> C compiler driver 92to get other “CPP” style preprocessing by giving the input file a 93‘<samp>.S</samp>’ suffix. <a href="https://gcc.gnu.org/onlinedocs/gcc/Overall-Options.html#Overall-Options">See the ’Options Controlling the Kind of Output’ section of the GCC manual for 94more details</a> 95</p> 96<p>Excess whitespace, comments, and character constants 97cannot be used in the portions of the input text that are not 98preprocessed. 99</p> 100<a name="index-turning-preprocessing-on-and-off"></a> 101<a name="index-preprocessing_002c-turning-on-and-off"></a> 102<a name="index-_0023NO_005fAPP"></a> 103<a name="index-_0023APP"></a> 104<p>If the first line of an input file is <code>#NO_APP</code> or if you use the 105‘<samp>-f</samp>’ option, whitespace and comments are not removed from the input file. 106Within an input file, you can ask for whitespace and comment removal in 107specific portions of the by putting a line that says <code>#APP</code> before the 108text that may contain whitespace or comments, and putting a line that says 109<code>#NO_APP</code> after this text. This feature is mainly intend to support 110<code>asm</code> statements in compilers whose output is otherwise free of comments 111and whitespace. 112</p> 113 114 115 116</body> 117</html> 118