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| <h3 class="section">4.25 <code>freopen</code>—open a file using an existing file descriptor</h3> |
| |
| <p><a name="index-freopen-196"></a><a name="index-g_t_005ffreopen_005fr-197"></a><strong>Synopsis</strong> |
| <pre class="example"> #include <stdio.h> |
| FILE *freopen(const char *<var>file</var>, const char *<var>mode</var>, |
| FILE *<var>fp</var>); |
| FILE *_freopen_r(struct _reent *<var>ptr</var>, const char *<var>file</var>, |
| const char *<var>mode</var>, FILE *<var>fp</var>); |
| |
| </pre> |
| <p><strong>Description</strong><br> |
| Use this variant of <code>fopen</code> if you wish to specify a particular file |
| descriptor <var>fp</var> (notably <code>stdin</code>, <code>stdout</code>, or <code>stderr</code>) for |
| the file. |
| |
| <p>If <var>fp</var> was associated with another file or stream, <code>freopen</code> |
| closes that other file or stream (but ignores any errors while closing |
| it). |
| |
| <p><var>file</var> and <var>mode</var> are used just as in <code>fopen</code>. |
| |
| <p>If <var>file</var> is <code>NULL</code>, the underlying stream is modified rather than |
| closed. The file cannot be given a more permissive access mode (for |
| example, a <var>mode</var> of "w" will fail on a read-only file descriptor), |
| but can change status such as append or binary mode. If modification |
| is not possible, failure occurs. |
| |
| <p><br> |
| <strong>Returns</strong><br> |
| If successful, the result is the same as the argument <var>fp</var>. If the |
| file cannot be opened as specified, the result is <code>NULL</code>. |
| |
| <p><br> |
| <strong>Portability</strong><br> |
| ANSI C requires <code>freopen</code>. |
| |
| <p>Supporting OS subroutines required: <code>close</code>, <code>fstat</code>, <code>isatty</code>, |
| <code>lseek</code>, <code>open</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>. |
| |
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