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  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

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  9. section entitled "GNU Free Documentation License".

  10. 

  11. This manual contains no Invariant Sections.  The Front-Cover Texts are

  12. (a) (see below), and the Back-Cover Texts are (b) (see below).

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  26. <title>Search Path (The C Preprocessor)</title>

  27. 

  28. <meta name="description" content="Search Path (The C Preprocessor)">

  29. <meta name="keywords" content="Search Path (The C Preprocessor)">

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  35. <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">

  36. <link href="Header-Files.html#Header-Files" rel="up" title="Header Files">

  37. <link href="Once_002dOnly-Headers.html#Once_002dOnly-Headers" rel="next" title="Once-Only Headers">

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  66. 

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  68. </head>

  69. 

  70. <body lang="en">

  71. <a name="Search-Path"></a>

  72. <div class="header">

  73. <p>

  74. Next: <a href="Once_002dOnly-Headers.html#Once_002dOnly-Headers" accesskey="n" rel="next">Once-Only Headers</a>, Previous: <a href="Include-Operation.html#Include-Operation" accesskey="p" rel="prev">Include Operation</a>, Up: <a href="Header-Files.html#Header-Files" accesskey="u" rel="up">Header Files</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>

  75. </div>

  76. <hr>

  77. <a name="Search-Path-1"></a>

  78. <h3 class="section">2.3 Search Path</h3>

  79. 

  80. <p>By default, the preprocessor looks for header files included by the quote

  81. form of the directive <code>#include&nbsp;&quot;<var>file</var>&quot;<!-- /@w --></code> first relative to

  82. the directory of the current file, and then in a preconfigured list 

  83. of standard system directories.  

  84. For example, if <samp>/usr/include/sys/stat.h</samp> contains

  85. <code>#include&nbsp;&quot;types.h&quot;<!-- /@w --></code>, GCC looks for <samp>types.h</samp> first in

  86. <samp>/usr/include/sys</samp>, then in its usual search path.

  87. </p>

  88. <p>For the angle-bracket form <code>#include&nbsp;&lt;<var>file</var>&gt;<!-- /@w --></code>, the

  89. preprocessor&rsquo;s default behavior is to look only in the standard system

  90. directories.  The exact search directory list depends on the target

  91. system, how GCC is configured, and where it is installed.  You can

  92. find the default search directory list for your version of CPP by

  93. invoking it with the <samp>-v</samp> option.  For example,

  94. </p>

  95. <div class="smallexample">

  96. <pre class="smallexample">cpp -v /dev/null -o /dev/null

  97. </pre></div>

  98. 

  99. <p>There are a number of command-line options you can use to add

  100. additional directories to the search path.  

  101. The most commonly-used option is <samp>-I<var>dir</var></samp>, which causes 

  102. <var>dir</var> to be searched after the current directory (for the quote 

  103. form of the directive) and ahead of the standard system directories.

  104. You can specify multiple <samp>-I</samp> options on the command line, 

  105. in which case the directories are searched in left-to-right order.

  106. </p>

  107. <p>If you need separate control over the search paths for the quote and 

  108. angle-bracket forms of the &lsquo;<samp>#include</samp>&rsquo; directive, you can use the

  109. <samp>-iquote</samp> and/or <samp>-isystem</samp> options instead of <samp>-I</samp>.

  110. See <a href="Invocation.html#Invocation">Invocation</a>, for a detailed description of these options, as 

  111. well as others that are less generally useful.

  112. </p>

  113. <p>If you specify other options on the command line, such as <samp>-I</samp>,

  114. that affect where the preprocessor searches for header files, the

  115. directory list printed by the <samp>-v</samp> option reflects the actual

  116. search path used by the preprocessor.

  117. </p>

  118. <p>Note that you can also prevent the preprocessor from searching any of

  119. the default system header directories with the <samp>-nostdinc</samp>

  120. option.  This is useful when you are compiling an operating system

  121. kernel or some other program that does not use the standard C library

  122. facilities, or the standard C library itself.

  123. </p>

  124. <hr>

  125. <div class="header">

  126. <p>

  127. Next: <a href="Once_002dOnly-Headers.html#Once_002dOnly-Headers" accesskey="n" rel="next">Once-Only Headers</a>, Previous: <a href="Include-Operation.html#Include-Operation" accesskey="p" rel="prev">Include Operation</a>, Up: <a href="Header-Files.html#Header-Files" accesskey="u" rel="up">Header Files</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p>

  128. </div>

  129. 

  130. 

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