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<h3 class="section">4.13 Preprocessing directives</h3>

<p>See <a href="../cpp/Implementation_002ddefined-behavior.html#Implementation_002ddefined-behavior">Implementation-defined behavior</a>, for details of these aspects of
implementation-defined behavior.

     <ul>
<li><cite>How sequences in both forms of header names are mapped to headers
or external source file names (C90 6.1.7, C99 6.4.7).</cite>

     <li><cite>Whether the value of a character constant in a constant expression
that controls conditional inclusion matches the value of the same character
constant in the execution character set (C90 6.8.1, C99 6.10.1).</cite>

     <li><cite>Whether the value of a single-character character constant in a
constant expression that controls conditional inclusion may have a
negative value (C90 6.8.1, C99 6.10.1).</cite>

     <li><cite>The places that are searched for an included &lsquo;</cite><samp><span class="samp">&lt;&gt;</span></samp><cite>&rsquo; delimited
header, and how the places are specified or the header is
identified (C90 6.8.2, C99 6.10.2).</cite>

     <li><cite>How the named source file is searched for in an included &lsquo;</cite><samp><span class="samp">""</span></samp><cite>&rsquo;
delimited header (C90 6.8.2, C99 6.10.2).</cite>

     <li><cite>The method by which preprocessing tokens (possibly resulting from
macro expansion) in a </cite><code>#include</code><cite> directive are combined into a header
name (C90 6.8.2, C99 6.10.2).</cite>

     <li><cite>The nesting limit for </cite><code>#include</code><cite> processing (C90 6.8.2, C99
6.10.2).</cite>

     <li><cite>Whether the &lsquo;</cite><samp><span class="samp">#</span></samp><cite>&rsquo; operator inserts a &lsquo;</cite><samp><span class="samp">\</span></samp><cite>&rsquo; character before
the &lsquo;</cite><samp><span class="samp">\</span></samp><cite>&rsquo; character that begins a universal character name in a
character constant or string literal (C99 6.10.3.2).</cite>

     <li><cite>The behavior on each recognized non-</cite><code>STDC #pragma</code><cite>
directive (C90 6.8.6, C99 6.10.6).</cite>

     <p>See <a href="../cpp/Pragmas.html#Pragmas">Pragmas</a>, for details of
pragmas accepted by GCC on all targets.  See <a href="Pragmas.html#Pragmas">Pragmas Accepted by GCC</a>, for details of target-specific pragmas.

     <li><cite>The definitions for </cite><code>__DATE__</code><cite> and </cite><code>__TIME__</code><cite> when
respectively, the date and time of translation are not available (C90
6.8.8, C99 6.10.8).</cite>

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