The Single UNIX ® Specification, Version 2
Copyright © 1997 The Open Group


fflush - flush a stream


#include <stdio.h>

int fflush(FILE *stream);


If stream points to an output stream or an update stream in which the most recent operation was not input, fflush() causes any unwritten data for that stream to be written to the file, and the st_ctime and st_mtime fields of the underlying file are marked for update.

If stream is a null pointer, fflush() performs this flushing action on all streams for which the behaviour is defined above.


Upon successful completion, fflush() returns 0. Otherwise, it returns EOF and sets errno to indicate the error.


The fflush() function will fail if:
The O_NONBLOCK flag is set for the file descriptor underlying stream and the process would be delayed in the write operation.
The file descriptor underlying stream is not valid.
An attempt was made to write a file that exceeds the maximum file size or the process' file size limit.
The file is a regular file and an attempt was made to write at or beyond the offset maximum associated with the corresponding stream.
The fflush() function was interrupted by a signal.
The process is a member of a background process group attempting to write to its controlling terminal, TOSTOP is set, the process is neither ignoring nor blocking SIGTTOU and the process group of the process is orphaned. This error may also be returned under implementation-dependent conditions.
There was no free space remaining on the device containing the file.
An attempt is made to write to a pipe or FIFO that is not open for reading by any process. A SIGPIPE signal will also be sent to the thread.

The fflush() function may fail if:

A request was made of a non-existent device, or the request was outside the capabilities of the device.








getrlimit(), ulimit(), <stdio.h>.


Derived from Issue 1 of the SVID.

UNIX ® is a registered Trademark of The Open Group.
Copyright © 1997 The Open Group
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