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| <h3 class="section">15.3 FIFO Special Files</h3> |
| |
| <p><a name="index-creating-a-FIFO-special-file-1626"></a><a name="index-interprocess-communication_002c-with-FIFO-1627"></a> |
| A FIFO special file is similar to a pipe, except that it is created in a |
| different way. Instead of being an anonymous communications channel, a |
| FIFO special file is entered into the file system by calling |
| <code>mkfifo</code>. |
| |
| <p>Once you have created a FIFO special file in this way, any process can |
| open it for reading or writing, in the same way as an ordinary file. |
| However, it has to be open at both ends simultaneously before you can |
| proceed to do any input or output operations on it. Opening a FIFO for |
| reading normally blocks until some other process opens the same FIFO for |
| writing, and vice versa. |
| |
| <p>The <code>mkfifo</code> function is declared in the header file |
| <samp><span class="file">sys/stat.h</span></samp>. |
| <a name="index-sys_002fstat_002eh-1628"></a> |
| <!-- sys/stat.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Function: int <b>mkfifo</b> (<var>const char *filename, mode_t mode</var>)<var><a name="index-mkfifo-1629"></a></var><br> |
| <blockquote><p>The <code>mkfifo</code> function makes a FIFO special file with name |
| <var>filename</var>. The <var>mode</var> argument is used to set the file's |
| permissions; see <a href="Setting-Permissions.html#Setting-Permissions">Setting Permissions</a>. |
| |
| <p>The normal, successful return value from <code>mkfifo</code> is <code>0</code>. In |
| the case of an error, <code>-1</code> is returned. In addition to the usual |
| file name errors (see <a href="File-Name-Errors.html#File-Name-Errors">File Name Errors</a>), the following |
| <code>errno</code> error conditions are defined for this function: |
| |
| <dl> |
| <dt><code>EEXIST</code><dd>The named file already exists. |
| |
| <br><dt><code>ENOSPC</code><dd>The directory or file system cannot be extended. |
| |
| <br><dt><code>EROFS</code><dd>The directory that would contain the file resides on a read-only file |
| system. |
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