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99 lines
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<title>Headers - GNU Compiler Collection (GCC) Internals</title>
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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``GNU Free Documentation License''.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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<a name="Headers"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Documentation.html#Documentation">Documentation</a>,
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Previous: <a rel="previous" accesskey="p" href="Library-Files.html#Library-Files">Library Files</a>,
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Up: <a rel="up" accesskey="u" href="gcc-Directory.html#gcc-Directory">gcc Directory</a>
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</div>
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<h4 class="subsection">6.3.6 Headers Installed by GCC</h4>
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<p>In general, GCC expects the system C library to provide most of the
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headers to be used with it. However, GCC will fix those headers if
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necessary to make them work with GCC, and will install some headers
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required of freestanding implementations. These headers are installed
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in <samp><var>libsubdir</var><span class="file">/include</span></samp>. Headers for non-C runtime
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libraries are also installed by GCC; these are not documented here.
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(FIXME: document them somewhere.)
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<p>Several of the headers GCC installs are in the <samp><span class="file">ginclude</span></samp>
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directory. These headers, <samp><span class="file">iso646.h</span></samp>,
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<samp><span class="file">stdarg.h</span></samp>, <samp><span class="file">stdbool.h</span></samp>, and <samp><span class="file">stddef.h</span></samp>,
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are installed in <samp><var>libsubdir</var><span class="file">/include</span></samp>,
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unless the target Makefile fragment (see <a href="Target-Fragment.html#Target-Fragment">Target Fragment</a>)
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overrides this by setting <code>USER_H</code>.
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<p>In addition to these headers and those generated by fixing system
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headers to work with GCC, some other headers may also be installed in
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<samp><var>libsubdir</var><span class="file">/include</span></samp>. <samp><span class="file">config.gcc</span></samp> may set
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<code>extra_headers</code>; this specifies additional headers under
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<samp><span class="file">config</span></samp> to be installed on some systems.
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<p>GCC installs its own version of <code><float.h></code>, from <samp><span class="file">ginclude/float.h</span></samp>.
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This is done to cope with command-line options that change the
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representation of floating point numbers.
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<p>GCC also installs its own version of <code><limits.h></code>; this is generated
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from <samp><span class="file">glimits.h</span></samp>, together with <samp><span class="file">limitx.h</span></samp> and
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<samp><span class="file">limity.h</span></samp> if the system also has its own version of
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<code><limits.h></code>. (GCC provides its own header because it is
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required of ISO C freestanding implementations, but needs to include
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the system header from its own header as well because other standards
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such as POSIX specify additional values to be defined in
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<code><limits.h></code>.) The system's <code><limits.h></code> header is used via
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<samp><var>libsubdir</var><span class="file">/include/syslimits.h</span></samp>, which is copied from
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<samp><span class="file">gsyslimits.h</span></samp> if it does not need fixing to work with GCC; if it
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needs fixing, <samp><span class="file">syslimits.h</span></samp> is the fixed copy.
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<p>GCC can also install <code><tgmath.h></code>. It will do this when
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<samp><span class="file">config.gcc</span></samp> sets <code>use_gcc_tgmath</code> to <code>yes</code>.
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