<html lang="en">
<head>
<title>Search Path - The C Preprocessor</title>
<meta http-equiv="Content-Type" content="text/html">
<meta name="description" content="The C Preprocessor">
<meta name="generator" content="makeinfo 4.13">
<link title="Top" rel="start" href="index.html#Top">
<link rel="up" href="Header-Files.html#Header-Files" title="Header Files">
<link rel="prev" href="Include-Operation.html#Include-Operation" title="Include Operation">
<link rel="next" href="Once_002dOnly-Headers.html#Once_002dOnly-Headers" title="Once-Only Headers">
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
<!--
Copyright (C) 1987-2015 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation. A copy of
the license is included in the
section entitled ``GNU Free Documentation License''.
This manual contains no Invariant Sections. The Front-Cover Texts are
(a) (see below), and the Back-Cover Texts are (b) (see below).
(a) The FSF's Front-Cover Text is:
A GNU Manual
(b) The FSF's Back-Cover Text is:
You have freedom to copy and modify this GNU Manual, like GNU
software. Copies published by the Free Software Foundation raise
funds for GNU development.
-->
<meta http-equiv="Content-Style-Type" content="text/css">
<style type="text/css"><!--
pre.display { font-family:inherit }
pre.format { font-family:inherit }
pre.smalldisplay { font-family:inherit; font-size:smaller }
pre.smallformat { font-family:inherit; font-size:smaller }
pre.smallexample { font-size:smaller }
pre.smalllisp { font-size:smaller }
span.sc { font-variant:small-caps }
span.roman { font-family:serif; font-weight:normal; }
span.sansserif { font-family:sans-serif; font-weight:normal; }
--></style>
</head>
<body>
<div class="node">
<a name="Search-Path"></a>
<p>
Next: <a rel="next" accesskey="n" href="Once_002dOnly-Headers.html#Once_002dOnly-Headers">Once-Only Headers</a>,
Previous: <a rel="previous" accesskey="p" href="Include-Operation.html#Include-Operation">Include Operation</a>,
Up: <a rel="up" accesskey="u" href="Header-Files.html#Header-Files">Header Files</a>
<hr>
</div>
<h3 class="section">2.3 Search Path</h3>
<p>GCC looks in several different places for headers. On a normal Unix
system, if you do not instruct it otherwise, it will look for headers
requested with <code>#include <</code><var>file</var><code>><!-- /@w --></code> in:
<pre class="smallexample"> /usr/local/include
<var>libdir</var>/gcc/<var>target</var>/<var>version</var>/include
/usr/<var>target</var>/include
/usr/include
</pre>
<p>For C++ programs, it will also look in
<samp><var>libdir</var><span class="file">/../include/c++/</span><var>version</var></samp>,
first. In the above, <var>target</var> is the canonical name of the system
GCC was configured to compile code for; often but not always the same as
the canonical name of the system it runs on. <var>version</var> is the
version of GCC in use.
<p>You can add to this list with the <samp><span class="option">-I</span><var>dir</var></samp> command-line
option. All the directories named by <samp><span class="option">-I</span></samp> are searched, in
left-to-right order, <em>before</em> the default directories. The only
exception is when <samp><span class="file">dir</span></samp> is already searched by default. In
this case, the option is ignored and the search order for system
directories remains unchanged.
<p>Duplicate directories are removed from the quote and bracket search
chains before the two chains are merged to make the final search chain.
Thus, it is possible for a directory to occur twice in the final search
chain if it was specified in both the quote and bracket chains.
<p>You can prevent GCC from searching any of the default directories with
the <samp><span class="option">-nostdinc</span></samp> option. This is useful when you are compiling an
operating system kernel or some other program that does not use the
standard C library facilities, or the standard C library itself.
<samp><span class="option">-I</span></samp> options are not ignored as described above when
<samp><span class="option">-nostdinc</span></samp> is in effect.
<p>GCC looks for headers requested with <code>#include "</code><var>file</var><code>"<!-- /@w --></code>
first in the directory containing the current file, then in the
directories as specified by <samp><span class="option">-iquote</span></samp> options, then in the same
places it would have looked for a header requested with angle
brackets. For example, if <samp><span class="file">/usr/include/sys/stat.h</span></samp> contains
<code>#include "types.h"<!-- /@w --></code>, GCC looks for <samp><span class="file">types.h</span></samp> first in
<samp><span class="file">/usr/include/sys</span></samp>, then in its usual search path.
<p>‘<samp><span class="samp">#line</span></samp>’ (see <a href="Line-Control.html#Line-Control">Line Control</a>) does not change GCC's idea of the
directory containing the current file.
<p>You may put <samp><span class="option">-I-</span></samp> at any point in your list of <samp><span class="option">-I</span></samp> options.
This has two effects. First, directories appearing before the
<samp><span class="option">-I-</span></samp> in the list are searched only for headers requested with
quote marks. Directories after <samp><span class="option">-I-</span></samp> are searched for all
headers. Second, the directory containing the current file is not
searched for anything, unless it happens to be one of the directories
named by an <samp><span class="option">-I</span></samp> switch. <samp><span class="option">-I-</span></samp> is deprecated, <samp><span class="option">-iquote</span></samp>
should be used instead.
<p><samp><span class="option">-I. -I-</span></samp> is not the same as no <samp><span class="option">-I</span></samp> options at all, and does
not cause the same behavior for ‘<samp><span class="samp"><></span></samp>’ includes that ‘<samp><span class="samp">""</span></samp>’
includes get with no special options. <samp><span class="option">-I.</span></samp> searches the
compiler's current working directory for header files. That may or may
not be the same as the directory containing the current file.
<p>If you need to look for headers in a directory named <samp><span class="file">-</span></samp>, write
<samp><span class="option">-I./-</span></samp>.
<p>There are several more ways to adjust the header search path. They are
generally less useful. See <a href="Invocation.html#Invocation">Invocation</a>.
</body></html>