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| <h3 class="section">2.1 Include Syntax</h3> |
| |
| <p><a name="index-g_t_0023include-27"></a>Both user and system header files are included using the preprocessing |
| directive ‘<samp><span class="samp">#include</span></samp>’. It has two variants: |
| |
| <dl> |
| <dt><code>#include <</code><var>file</var><code>></code><dd>This variant is used for system header files. It searches for a file |
| named <var>file</var> in a standard list of system directories. You can prepend |
| directories to this list with the <samp><span class="option">-I</span></samp> option (see <a href="Invocation.html#Invocation">Invocation</a>). |
| |
| <br><dt><code>#include "</code><var>file</var><code>"</code><dd>This variant is used for header files of your own program. It |
| searches for a file named <var>file</var> first in the directory containing |
| the current file, then in the quote directories and then the same |
| directories used for <code><</code><var>file</var><code>></code>. You can prepend directories |
| to the list of quote directories with the <samp><span class="option">-iquote</span></samp> option. |
| </dl> |
| |
| <p>The argument of ‘<samp><span class="samp">#include</span></samp>’, whether delimited with quote marks or |
| angle brackets, behaves like a string constant in that comments are not |
| recognized, and macro names are not expanded. Thus, <code>#include <x/*y><!-- /@w --></code> specifies inclusion of a system header file named <samp><span class="file">x/*y</span></samp>. |
| |
| <p>However, if backslashes occur within <var>file</var>, they are considered |
| ordinary text characters, not escape characters. None of the character |
| escape sequences appropriate to string constants in C are processed. |
| Thus, <code>#include "x\n\\y"<!-- /@w --></code> specifies a filename containing three |
| backslashes. (Some systems interpret ‘<samp><span class="samp">\</span></samp>’ as a pathname separator. |
| All of these also interpret ‘<samp><span class="samp">/</span></samp>’ the same way. It is most portable |
| to use only ‘<samp><span class="samp">/</span></samp>’.) |
| |
| <p>It is an error if there is anything (other than comments) on the line |
| after the file name. |
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