fflush - flush a stream
#include <stdio.h>
int fflush(FILE *stream);
For output streams,
fflush() forces a write of all user-space buffered
data for the given output or update
stream via the stream's underlying
write function.
For input streams associated with seekable files (e.g., disk files, but not
pipes or terminals),
fflush() discards any buffered data that has been
fetched from the underlying file, but has not been consumed by the
application.
The open status of the stream is unaffected.
If the
stream argument is NULL,
fflush() flushes
all open
output streams.
For a nonlocking counterpart, see
unlocked_stdio(3).
Upon successful completion 0 is returned. Otherwise,
EOF is returned and
errno is set to indicate the error.
- EBADF
- stream is not an open stream, or is not open for writing.
The function
fflush() may also fail and set
errno for any of the
errors specified for
write(2).
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
fflush () |
Thread safety |
MT-Safe |
C89, C99, POSIX.1-2001, POSIX.1-2008.
POSIX.1-2001 did not specify the behavior for flushing of input streams, but the
behavior is specified in POSIX.1-2008.
Note that
fflush() flushes only the user-space buffers provided by the C
library. To ensure that the data is physically stored on disk the kernel
buffers must be flushed too, for example, with
sync(2) or
fsync(2).
fsync(2),
sync(2),
write(2),
fclose(3),
fileno(3),
fopen(3),
setbuf(3),
unlocked_stdio(3)