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 <a name="Traditional-lexical-analysis"></a>
 <div class="header">
 <p>
 Next: <a href="Traditional-macros.html#Traditional-macros" accesskey="n" rel="next">Traditional macros</a>, Up: <a href="Traditional-Mode.html#Traditional-Mode" accesskey="u" rel="up">Traditional Mode</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="Traditional-lexical-analysis-1"></a>
 <h3 class="section">10.1 Traditional lexical analysis</h3>

 <p>The traditional preprocessor does not decompose its input into tokens
 the same way a standards-conforming preprocessor does.  The input is
 simply treated as a stream of text with minimal internal form.
 </p>
 <p>This implementation does not treat trigraphs (see <a href="Initial-processing.html#trigraphs">trigraphs</a>)
 specially since they were an invention of the standards committee.  It
 handles arbitrarily-positioned escaped newlines properly and splices
 the lines as you would expect; many traditional preprocessors did not
 do this.
 </p>
 <p>The form of horizontal whitespace in the input file is preserved in
 the output.  In particular, hard tabs remain hard tabs.  This can be
 useful if, for example, you are preprocessing a Makefile.
 </p>
 <p>Traditional CPP only recognizes C-style block comments, and treats the
 &lsquo;<samp>/*</samp>&rsquo; sequence as introducing a comment only if it lies outside
 quoted text.  Quoted text is introduced by the usual single and double
 quotes, and also by an initial &lsquo;<samp>&lt;</samp>&rsquo; in a <code>#include</code>
 directive.
 </p>
 <p>Traditionally, comments are completely removed and are not replaced
 with a space.  Since a traditional compiler does its own tokenization
 of the output of the preprocessor, this means that comments can
 effectively be used as token paste operators.  However, comments
 behave like separators for text handled by the preprocessor itself,
 since it doesn&rsquo;t re-lex its input.  For example, in
 </p>
 <div class="smallexample">
 <pre class="smallexample">#if foo/**/bar
 </pre></div>

 <p>&lsquo;<samp>foo</samp>&rsquo; and &lsquo;<samp>bar</samp>&rsquo; are distinct identifiers and expanded
 separately if they happen to be macros.  In other words, this
 directive is equivalent to
 </p>
 <div class="smallexample">
 <pre class="smallexample">#if foo bar
 </pre></div>

 <p>rather than
 </p>
 <div class="smallexample">
 <pre class="smallexample">#if foobar
 </pre></div>

 <p>Generally speaking, in traditional mode an opening quote need not have
 a matching closing quote.  In particular, a macro may be defined with
 replacement text that contains an unmatched quote.  Of course, if you
 attempt to compile preprocessed output containing an unmatched quote
 you will get a syntax error.
 </p>
 <p>However, all preprocessing directives other than <code>#define</code>
 require matching quotes.  For example:
 </p>
 <div class="smallexample">
 <pre class="smallexample">#define m This macro's fine and has an unmatched quote
 &quot;/* This is not a comment.  */
 /* <span class="roman">This is a comment.  The following #include directive
    is ill-formed.</span>  */
 #include &lt;stdio.h
 </pre></div>

 <p>Just as for the ISO preprocessor, what would be a closing quote can be
 escaped with a backslash to prevent the quoted text from closing.
 </p>
 <hr>
 <div class="header">
 <p>
 Next: <a href="Traditional-macros.html#Traditional-macros" accesskey="n" rel="next">Traditional macros</a>, Up: <a href="Traditional-Mode.html#Traditional-Mode" accesskey="u" rel="up">Traditional Mode</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
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	<title>The C Preprocessor: Traditional lexical analysis</title>

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	<a name="Traditional-lexical-analysis"></a>
	<div class="header">
	<p>
	Next: <a href="Traditional-macros.html#Traditional-macros" accesskey="n" rel="next">Traditional macros</a>, Up: <a href="Traditional-Mode.html#Traditional-Mode" accesskey="u" rel="up">Traditional Mode</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
	</div>
	<hr>
	<a name="Traditional-lexical-analysis-1"></a>
	<h3 class="section">10.1 Traditional lexical analysis</h3>

	<p>The traditional preprocessor does not decompose its input into tokens
	the same way a standards-conforming preprocessor does. The input is
	simply treated as a stream of text with minimal internal form.
	</p>
	<p>This implementation does not treat trigraphs (see <a href="Initial-processing.html#trigraphs">trigraphs</a>)
	specially since they were an invention of the standards committee. It
	handles arbitrarily-positioned escaped newlines properly and splices
	the lines as you would expect; many traditional preprocessors did not
	do this.
	</p>
	<p>The form of horizontal whitespace in the input file is preserved in
	the output. In particular, hard tabs remain hard tabs. This can be
	useful if, for example, you are preprocessing a Makefile.
	</p>
	<p>Traditional CPP only recognizes C-style block comments, and treats the
	‘<samp>/*</samp>’ sequence as introducing a comment only if it lies outside
	quoted text. Quoted text is introduced by the usual single and double
	quotes, and also by an initial ‘<samp><</samp>’ in a <code>#include</code>
	directive.
	</p>
	<p>Traditionally, comments are completely removed and are not replaced
	with a space. Since a traditional compiler does its own tokenization
	of the output of the preprocessor, this means that comments can
	effectively be used as token paste operators. However, comments
	behave like separators for text handled by the preprocessor itself,
	since it doesn’t re-lex its input. For example, in
	</p>
	<div class="smallexample">
	<pre class="smallexample">#if foo/**/bar
	</pre></div>

	<p>‘<samp>foo</samp>’ and ‘<samp>bar</samp>’ are distinct identifiers and expanded
	separately if they happen to be macros. In other words, this
	directive is equivalent to
	</p>
	<div class="smallexample">
	<pre class="smallexample">#if foo bar
	</pre></div>

	<p>rather than
	</p>
	<div class="smallexample">
	<pre class="smallexample">#if foobar
	</pre></div>

	<p>Generally speaking, in traditional mode an opening quote need not have
	a matching closing quote. In particular, a macro may be defined with
	replacement text that contains an unmatched quote. Of course, if you
	attempt to compile preprocessed output containing an unmatched quote
	you will get a syntax error.
	</p>
	<p>However, all preprocessing directives other than <code>#define</code>
	require matching quotes. For example:
	</p>
	<div class="smallexample">
	<pre class="smallexample">#define m This macro's fine and has an unmatched quote
	"/* This is not a comment. */
	/* <span class="roman">This is a comment. The following #include directive
	is ill-formed.</span> */
	#include <stdio.h
	</pre></div>

	<p>Just as for the ISO preprocessor, what would be a closing quote can be
	escaped with a backslash to prevent the quoted text from closing.
	</p>
	<hr>
	<div class="header">
	<p>
	Next: <a href="Traditional-macros.html#Traditional-macros" accesskey="n" rel="next">Traditional macros</a>, Up: <a href="Traditional-Mode.html#Traditional-Mode" accesskey="u" rel="up">Traditional Mode</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>
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