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<a name="Fixed-Header-Files"></a>
<h3 class="section">14.4 Fixed Header Files</h3>

<p>GCC needs to install corrected versions of some system header files.
This is because most target systems have some header files that won&rsquo;t
work with GCC unless they are changed.  Some have bugs, some are
incompatible with ISO C, and some depend on special features of other
compilers.
</p>
<p>Installing GCC automatically creates and installs the fixed header
files, by running a program called <code>fixincludes</code>.  Normally, you
don&rsquo;t need to pay attention to this.  But there are cases where it
doesn&rsquo;t do the right thing automatically.
</p>
<ul>
<li> If you update the system&rsquo;s header files, such as by installing a new
system version, the fixed header files of GCC are not automatically
updated.  They can be updated using the <code>mkheaders</code> script
installed in
<samp><var>libexecdir</var>/gcc/<var>target</var>/<var>version</var>/install-tools/</samp>.

</li><li> On some systems, header file directories contain
machine-specific symbolic links in certain places.  This makes it
possible to share most of the header files among hosts running the
same version of the system on different machine models.

<p>The programs that fix the header files do not understand this special
way of using symbolic links; therefore, the directory of fixed header
files is good only for the machine model used to build it.
</p>
<p>It is possible to make separate sets of fixed header files for the
different machine models, and arrange a structure of symbolic links so
as to use the proper set, but you&rsquo;ll have to do this by hand.
</p></li></ul>


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