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<title>Using the GNU Compiler Collection (GCC)</title>
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Node:<a name="Directory%20Options">Directory Options</a>,
Next:<a rel="next" accesskey="n" href="Spec-Files.html#Spec%20Files">Spec Files</a>,
Previous:<a rel="previous" accesskey="p" href="Link-Options.html#Link%20Options">Link Options</a>,
Up:<a rel="up" accesskey="u" href="Invoking-GCC.html#Invoking%20GCC">Invoking GCC</a>
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<h3 class="section">Options for Directory Search</h3>
<p>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><code></code>
<dd>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 <code>-isystem</code> for that). If you use more than
one <code>-I</code> 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
<code>-isystem</code>, is also specified with <code>-I</code>, the <code>-I</code>
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 <code>-nostdinc</code> and/or <code>-isystem</code> options.
<br><dt><code>-I-</code>
<dd>Any directories you specify with <code>-I</code> options before the <code>-I-</code>
option are searched only for the case of <code>#include "</code><var>file</var><code>"</code>;
they are not searched for <code>#include <</code><var>file</var><code>></code>.
<p>If additional directories are specified with <code>-I</code> options after
the <code>-I-</code>, these directories are searched for all <code>#include</code>
directives. (Ordinarily <em>all</em> <code>-I</code> directories are used
this way.)
<p>In addition, the <code>-I-</code> option inhibits the use of the current
directory (where the current input file came from) as the first search
directory for <code>#include "</code><var>file</var><code>"</code>. There is no way to
override this effect of <code>-I-</code>. With <code>-I.</code> 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><code>-I-</code> does not inhibit the use of the standard system directories
for header files. Thus, <code>-I-</code> and <code>-nostdinc</code> are
independent.
<br><dt><code>-L</code><var>dir</var><code></code>
<dd>Add directory <var>dir</var> to the list of directories to be searched
for <code>-l</code>.
<br><dt><code>-B</code><var>prefix</var><code></code>
<dd>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
<code>cpp</code>, <code>cc1</code>, <code>as</code> and <code>ld</code>. It tries
<var>prefix</var> as a prefix for each program it tries to run, both with and
without <code></code><var>machine</var><code>/</code><var>version</var><code>/</code> (see <a href="Target-Options.html#Target%20Options">Target Options</a>).
<p>For each subprogram to be run, the compiler driver first tries the
<code>-B</code> prefix, if any. If that name is not found, or if <code>-B</code>
was not specified, the driver tries two standard prefixes, which are
<code>/usr/lib/gcc/</code> and <code>/usr/local/lib/gcc-lib/</code>. 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
<code>PATH</code> environment variable.
<p>The compiler will check to see if the path provided by the <code>-B</code>
refers to a directory, and if necessary it will add a directory
separator character at the end of the path.
<p><code>-B</code> prefixes that effectively specify directory names also apply
to libraries in the linker, because the compiler translates these
options into <code>-L</code> options for the linker. They also apply to
includes files in the preprocessor, because the compiler translates these
options into <code>-isystem</code> options for the preprocessor. In this case,
the compiler appends <code>include</code> to the prefix.
<p>The run-time support file <code>libgcc.a</code> can also be searched for using
the <code>-B</code> 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 <code>-B</code> prefix is to use
the environment variable <code>GCC_EXEC_PREFIX</code>. See <a href="Environment-Variables.html#Environment%20Variables">Environment Variables</a>.
<p>As a special kludge, if the path provided by <code>-B</code> is
<code>[dir/]stage</code><var>N</var><code>/</code>, where <var>N</var> is a number in the range 0 to
9, then it will be replaced by <code>[dir/]include</code>. This is to help
with boot-strapping the compiler.
<br><dt><code>-specs=</code><var>file</var><code></code>
<dd>Process <var>file</var> after the compiler reads in the standard <code>specs</code>
file, in order to override the defaults that the <code>gcc</code> driver
program uses when determining what switches to pass to <code>cc1</code>,
<code>cc1plus</code>, <code>as</code>, <code>ld</code>, etc. More than one
<code>-specs=</code><var>file</var><code></code> can be specified on the command line, and they
are processed in order, from left to right.
</dl>
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