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<h1 class="settitle" align="center">The GNU C Preprocessor Internals</h1>


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  <li><a name="toc-Cpplib_002d_002d_002dthe-GNU-C-Preprocessor" href="#Cpplib_002d_002d_002dthe-GNU-C-Preprocessor">1 Cpplib&mdash;the GNU C Preprocessor</a></li>
  <li><a name="toc-Conventions-1" href="Conventions.html#Conventions">Conventions</a></li>
  <li><a name="toc-The-Lexer" href="Lexer.html#Lexer">The Lexer</a>
  <ul class="no-bullet">
    <li><a name="toc-Overview" href="Lexer.html#Overview">Overview</a></li>
    <li><a name="toc-Lexing-a-token" href="Lexer.html#Lexing-a-token">Lexing a token</a></li>
    <li><a name="toc-Lexing-a-line-1" href="Lexer.html#Lexing-a-line-1">Lexing a line</a></li>
  </ul></li>
  <li><a name="toc-Hash-Nodes-1" href="Hash-Nodes.html#Hash-Nodes">Hash Nodes</a></li>
  <li><a name="toc-Macro-Expansion-Algorithm" href="Macro-Expansion.html#Macro-Expansion">Macro Expansion Algorithm</a>
  <ul class="no-bullet">
    <li><a name="toc-Internal-representation-of-macros" href="Macro-Expansion.html#Internal-representation-of-macros">Internal representation of macros</a></li>
    <li><a name="toc-Macro-expansion-overview" href="Macro-Expansion.html#Macro-expansion-overview">Macro expansion overview</a></li>
    <li><a name="toc-Scanning-the-replacement-list-for-macros-to-expand" href="Macro-Expansion.html#Scanning-the-replacement-list-for-macros-to-expand">Scanning the replacement list for macros to expand</a></li>
    <li><a name="toc-Looking-for-a-function_002dlike-macro_0027s-opening-parenthesis" href="Macro-Expansion.html#Looking-for-a-function_002dlike-macro_0027s-opening-parenthesis">Looking for a function-like macro&rsquo;s opening parenthesis</a></li>
    <li><a name="toc-Marking-tokens-ineligible-for-future-expansion" href="Macro-Expansion.html#Marking-tokens-ineligible-for-future-expansion">Marking tokens ineligible for future expansion</a></li>
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  <li><a name="toc-Token-Spacing-1" href="Token-Spacing.html#Token-Spacing">Token Spacing</a></li>
  <li><a name="toc-Line-numbering" href="Line-Numbering.html#Line-Numbering">Line numbering</a>
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    <li><a name="toc-Just-which-line-number-anyway_003f" href="Line-Numbering.html#Just-which-line-number-anyway_003f">Just which line number anyway?</a></li>
    <li><a name="toc-Representation-of-line-numbers" href="Line-Numbering.html#Representation-of-line-numbers">Representation of line numbers</a></li>
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  <li><a name="toc-The-Multiple_002dInclude-Optimization" href="Guard-Macros.html#Guard-Macros">The Multiple-Include Optimization</a></li>
  <li><a name="toc-File-Handling" href="Files.html#Files">File Handling</a></li>
  <li><a name="toc-Concept-Index-1" href="Concept-Index.html#Concept-Index">Concept Index</a></li>
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Next: <a href="Conventions.html#Conventions" accesskey="n" rel="next">Conventions</a>, Up: <a href="../dir/index.html" accesskey="u" rel="up">(dir)</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<tr><td align="left" valign="top">&bull; <a href="Conventions.html#Conventions" accesskey="1">Conventions</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Lexer.html#Lexer" accesskey="2">Lexer</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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<tr><td align="left" valign="top">&bull; <a href="Hash-Nodes.html#Hash-Nodes" accesskey="3">Hash Nodes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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<tr><td align="left" valign="top">&bull; <a href="Macro-Expansion.html#Macro-Expansion" accesskey="4">Macro Expansion</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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<tr><td align="left" valign="top">&bull; <a href="Token-Spacing.html#Token-Spacing" accesskey="5">Token Spacing</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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<tr><td align="left" valign="top">&bull; <a href="Line-Numbering.html#Line-Numbering" accesskey="6">Line Numbering</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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<tr><td align="left" valign="top">&bull; <a href="Guard-Macros.html#Guard-Macros" accesskey="7">Guard Macros</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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<tr><td align="left" valign="top">&bull; <a href="Files.html#Files" accesskey="8">Files</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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<tr><td align="left" valign="top">&bull; <a href="Concept-Index.html#Concept-Index" accesskey="9">Concept Index</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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<a name="Cpplib_002d_002d_002dthe-GNU-C-Preprocessor"></a>
<h2 class="chapter">1 Cpplib&mdash;the GNU C Preprocessor</h2>

<p>The GNU C preprocessor is
implemented as a library, <em>cpplib</em>, so it can be easily shared between
a stand-alone preprocessor, and a preprocessor integrated with the C,
C++ and Objective-C front ends.  It is also available for use by other
programs, though this is not recommended as its exposed interface has
not yet reached a point of reasonable stability.
</p>
<p>The library has been written to be re-entrant, so that it can be used
to preprocess many files simultaneously if necessary.  It has also been
written with the preprocessing token as the fundamental unit; the
preprocessor in previous versions of GCC would operate on text strings
as the fundamental unit.
</p>
<p>This brief manual documents the internals of cpplib, and explains some
of the tricky issues.  It is intended that, along with the comments in
the source code, a reasonably competent C programmer should be able to
figure out what the code is doing, and why things have been implemented
the way they have.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="Conventions.html#Conventions" accesskey="1">Conventions</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Conventions used in the code.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Lexer.html#Lexer" accesskey="2">Lexer</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">The combined C, C++ and Objective-C Lexer.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Hash-Nodes.html#Hash-Nodes" accesskey="3">Hash Nodes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">All identifiers are entered into a hash table.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Macro-Expansion.html#Macro-Expansion" accesskey="4">Macro Expansion</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Macro expansion algorithm.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Token-Spacing.html#Token-Spacing" accesskey="5">Token Spacing</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Spacing and paste avoidance issues.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Line-Numbering.html#Line-Numbering" accesskey="6">Line Numbering</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Tracking location within files.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Guard-Macros.html#Guard-Macros" accesskey="7">Guard Macros</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Optimizing header files with guard macros.
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Files.html#Files" accesskey="8">Files</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">File handling.
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<tr><td align="left" valign="top">&bull; <a href="Concept-Index.html#Concept-Index" accesskey="9">Concept Index</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Index.
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