FFLUSH(3C) Standard C Library Functions FFLUSH(3C)

NAME

fflush - flush a stream

SYNOPSIS

#include <stdio.h>

int fflush(FILE *stream);

DESCRIPTION

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 points to an input stream or an update stream into which the
most recent operation was input, that stream is flushed if it is seekable
and is not already at end-of-file. Flushing an input stream discards any
buffered input and adjusts the file pointer such that the next input
operation accesses the byte after the last one read. A stream is
seekable if the underlying file is not a pipe, FIFO, socket, or TTY
device.


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


An input stream, seekable or non-seekable, can be flushed by explicitly
calling fflush() with a non-null argument specifying that stream.

RETURN VALUES

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

ERRORS

The fflush() function will fail if:

EAGAIN
The O_NONBLOCK flag is set for the file descriptor underlying
stream and the process would be delayed in the write operation.


EBADF
The file descriptor underlying stream is not valid.


EFBIG
An attempt was made to write a file that exceeds the maximum
file size or the process's file size limit; or the file is a
regular file and an attempt was made to write at or beyond the
offset maximum associated with the corresponding stream.


EINTR
The fflush() function was interrupted by a signal.


EIO
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. stream was created
by open_wmemstream(3C) and a wide-character or byte sequence
buffered is invalid in the current locale.


ENOSPC
There was no free space remaining on the device containing the
file.


EPIPE
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 calling process.


The fflush() function may fail if:

ENXIO
A request was made of a non-existent device, or the request was
beyond the limits of the device.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO

getrlimit(2), ulimit(2), attributes(7), standards(7)

March 25, 2020 FFLUSH(3C)