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<h3 class="section">3.14 Options for Directory Search</h3>

<p><a name="index-directory-options-998"></a><a name="index-options_002c-directory-search-999"></a><a name="index-search-path-1000"></a>
These options specify directories to search for header files, for
libraries and for parts of the compiler:

     <dl>
<dt><code>-I</code><var>dir</var><dd><a name="index-I-1001"></a>Add the directory <var>dir</var> to the head of the list of directories to be
searched for header files.  This can be used to override a system header
file, substituting your own version, since these directories are
searched before the system header file directories.  However, you should
not use this option to add directories that contain vendor-supplied
system header files (use <samp><span class="option">-isystem</span></samp> for that).  If you use more than
one <samp><span class="option">-I</span></samp> option, the directories are scanned in left-to-right
order; the standard system directories come after.

     <p>If a standard system include directory, or a directory specified with
<samp><span class="option">-isystem</span></samp>, is also specified with <samp><span class="option">-I</span></samp>, the <samp><span class="option">-I</span></samp>
option will be ignored.  The directory will still be searched but as a
system directory at its normal position in the system include chain.
This is to ensure that GCC's procedure to fix buggy system headers and
the ordering for the include_next directive are not inadvertently changed.
If you really need to change the search order for system directories,
use the <samp><span class="option">-nostdinc</span></samp> and/or <samp><span class="option">-isystem</span></samp> options.

     <br><dt><code>-iplugindir=</code><var>dir</var><dd>Set the directory to search for plugins which are passed
by <samp><span class="option">-fplugin=</span><var>name</var></samp> instead of
<samp><span class="option">-fplugin=</span><var>path</var><span class="option">/</span><var>name</var><span class="option">.so</span></samp>.  This option is not meant
to be used by the user, but only passed by the driver.

     <br><dt><code>-iquote</code><var>dir</var><dd><a name="index-iquote-1002"></a>Add the directory <var>dir</var> to the head of the list of directories to
be searched for header files only for the case of &lsquo;<samp><span class="samp">#include
"</span><var>file</var><span class="samp">"</span></samp>&rsquo;; they are not searched for &lsquo;<samp><span class="samp">#include &lt;</span><var>file</var><span class="samp">&gt;</span></samp>&rsquo;,
otherwise just like <samp><span class="option">-I</span></samp>.

     <br><dt><code>-L</code><var>dir</var><dd><a name="index-L-1003"></a>Add directory <var>dir</var> to the list of directories to be searched
for <samp><span class="option">-l</span></samp>.

     <br><dt><code>-B</code><var>prefix</var><dd><a name="index-B-1004"></a>This option specifies where to find the executables, libraries,
include files, and data files of the compiler itself.

     <p>The compiler driver program runs one or more of the subprograms
<samp><span class="file">cpp</span></samp>, <samp><span class="file">cc1</span></samp>, <samp><span class="file">as</span></samp> and <samp><span class="file">ld</span></samp>.  It tries
<var>prefix</var> as a prefix for each program it tries to run, both with and
without &lsquo;<samp><var>machine</var><span class="samp">/</span><var>version</var><span class="samp">/</span></samp>&rsquo; (see <a href="Target-Options.html#Target-Options">Target Options</a>).

     <p>For each subprogram to be run, the compiler driver first tries the
<samp><span class="option">-B</span></samp> prefix, if any.  If that name is not found, or if <samp><span class="option">-B</span></samp>
was not specified, the driver tries two standard prefixes, which are
<samp><span class="file">/usr/lib/gcc/</span></samp> and <samp><span class="file">/usr/local/lib/gcc/</span></samp>.  If neither of
those results in a file name that is found, the unmodified program
name is searched for using the directories specified in your
<samp><span class="env">PATH</span></samp> environment variable.

     <p>The compiler will check to see if the path provided by the <samp><span class="option">-B</span></samp>
refers to a directory, and if necessary it will add a directory
separator character at the end of the path.

     <p><samp><span class="option">-B</span></samp> prefixes that effectively specify directory names also apply
to libraries in the linker, because the compiler translates these
options into <samp><span class="option">-L</span></samp> options for the linker.  They also apply to
includes files in the preprocessor, because the compiler translates these
options into <samp><span class="option">-isystem</span></samp> options for the preprocessor.  In this case,
the compiler appends &lsquo;<samp><span class="samp">include</span></samp>&rsquo; to the prefix.

     <p>The run-time support file <samp><span class="file">libgcc.a</span></samp> can also be searched for using
the <samp><span class="option">-B</span></samp> prefix, if needed.  If it is not found there, the two
standard prefixes above are tried, and that is all.  The file is left
out of the link if it is not found by those means.

     <p>Another way to specify a prefix much like the <samp><span class="option">-B</span></samp> prefix is to use
the environment variable <samp><span class="env">GCC_EXEC_PREFIX</span></samp>.  See <a href="Environment-Variables.html#Environment-Variables">Environment Variables</a>.

     <p>As a special kludge, if the path provided by <samp><span class="option">-B</span></samp> is
<samp><span class="file">[dir/]stage</span><var>N</var><span class="file">/</span></samp>, where <var>N</var> is a number in the range 0 to
9, then it will be replaced by <samp><span class="file">[dir/]include</span></samp>.  This is to help
with boot-strapping the compiler.

     <br><dt><code>-specs=</code><var>file</var><dd><a name="index-specs-1005"></a>Process <var>file</var> after the compiler reads in the standard <samp><span class="file">specs</span></samp>
file, in order to override the defaults that the <samp><span class="file">gcc</span></samp> driver
program uses when determining what switches to pass to <samp><span class="file">cc1</span></samp>,
<samp><span class="file">cc1plus</span></samp>, <samp><span class="file">as</span></samp>, <samp><span class="file">ld</span></samp>, etc.  More than one
<samp><span class="option">-specs=</span><var>file</var></samp> can be specified on the command line, and they
are processed in order, from left to right.

     <br><dt><code>--sysroot=</code><var>dir</var><dd><a name="index-sysroot-1006"></a>Use <var>dir</var> as the logical root directory for headers and libraries.
For example, if the compiler would normally search for headers in
<samp><span class="file">/usr/include</span></samp> and libraries in <samp><span class="file">/usr/lib</span></samp>, it will instead
search <samp><var>dir</var><span class="file">/usr/include</span></samp> and <samp><var>dir</var><span class="file">/usr/lib</span></samp>.

     <p>If you use both this option and the <samp><span class="option">-isysroot</span></samp> option, then
the <samp><span class="option">--sysroot</span></samp> option will apply to libraries, but the
<samp><span class="option">-isysroot</span></samp> option will apply to header files.

     <p>The GNU linker (beginning with version 2.16) has the necessary support
for this option.  If your linker does not support this option, the
header file aspect of <samp><span class="option">--sysroot</span></samp> will still work, but the
library aspect will not.

     <br><dt><code>-I-</code><dd><a name="index-I_002d-1007"></a>This option has been deprecated.  Please use <samp><span class="option">-iquote</span></samp> instead for
<samp><span class="option">-I</span></samp> directories before the <samp><span class="option">-I-</span></samp> and remove the <samp><span class="option">-I-</span></samp>.
Any directories you specify with <samp><span class="option">-I</span></samp> options before the <samp><span class="option">-I-</span></samp>
option are searched only for the case of &lsquo;<samp><span class="samp">#include "</span><var>file</var><span class="samp">"</span></samp>&rsquo;;
they are not searched for &lsquo;<samp><span class="samp">#include &lt;</span><var>file</var><span class="samp">&gt;</span></samp>&rsquo;.

     <p>If additional directories are specified with <samp><span class="option">-I</span></samp> options after
the <samp><span class="option">-I-</span></samp>, these directories are searched for all &lsquo;<samp><span class="samp">#include</span></samp>&rsquo;
directives.  (Ordinarily <em>all</em> <samp><span class="option">-I</span></samp> directories are used
this way.)

     <p>In addition, the <samp><span class="option">-I-</span></samp> option inhibits the use of the current
directory (where the current input file came from) as the first search
directory for &lsquo;<samp><span class="samp">#include "</span><var>file</var><span class="samp">"</span></samp>&rsquo;.  There is no way to
override this effect of <samp><span class="option">-I-</span></samp>.  With <samp><span class="option">-I.</span></samp> you can specify
searching the directory which was current when the compiler was
invoked.  That is not exactly the same as what the preprocessor does
by default, but it is often satisfactory.

     <p><samp><span class="option">-I-</span></samp> does not inhibit the use of the standard system directories
for header files.  Thus, <samp><span class="option">-I-</span></samp> and <samp><span class="option">-nostdinc</span></samp> are
independent.
</dl>

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