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| <h3 class="section">4.9 <code>fflush</code>—flush buffered file output</h3> |
| |
| <p><a name="index-fflush-162"></a><a name="index-g_t_005ffflush_005fr-163"></a><strong>Synopsis</strong> |
| <pre class="example"> #include <stdio.h> |
| int fflush(FILE *<var>fp</var>); |
| |
| int _fflush_r(struct _reent *<var>reent</var>, FILE *<var>fp</var>); |
| |
| </pre> |
| <p><strong>Description</strong><br> |
| The <code>stdio</code> output functions can buffer output before delivering it |
| to the host system, in order to minimize the overhead of system calls. |
| |
| <p>Use <code>fflush</code> to deliver any such pending output (for the file |
| or stream identified by <var>fp</var>) to the host system. |
| |
| <p>If <var>fp</var> is <code>NULL</code>, <code>fflush</code> delivers pending output from all |
| open files. |
| |
| <p>Additionally, if <var>fp</var> is a seekable input stream visiting a file |
| descriptor, set the position of the file descriptor to match next |
| unread byte, useful for obeying POSIX semantics when ending a process |
| without consuming all input from the stream. |
| |
| <p>The alternate function <code>_fflush_r</code> is a reentrant version, where the |
| extra argument <var>reent</var> is a pointer to a reentrancy structure, and |
| <var>fp</var> must not be NULL. |
| |
| <p><br> |
| <strong>Returns</strong><br> |
| <code>fflush</code> returns <code>0</code> unless it encounters a write error; in that |
| situation, it returns <code>EOF</code>. |
| |
| <p><br> |
| <strong>Portability</strong><br> |
| ANSI C requires <code>fflush</code>. The behavior on input streams is only |
| specified by POSIX, and not all implementations follow POSIX rules. |
| |
| <p>No supporting OS subroutines are required. |
| |
| <p><br> |
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