FFLUSH(3C)FFLUSH(3C)NAMEfflush - flush a stream
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 points to an input stream or an update stream into which the
most recent operation was input, that stream is flushed if it is seek‐
able and is not already at end-of-file. Flushing an input stream dis‐
cards 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.
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 opera‐
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'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.
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.
There was no free space remaining on the device containing
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:
A request was made of a non-existent device, or the request
was beyond the limits of the device.
See attributes(5) for descriptions of the following attributes:
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│Interface Stability │ Standard │
│MT-Level │ MT-Safe │
SEE ALSOgetrlimit(2), ulimit(2), attributes(5), standards(5)
Nov 1, 2003 FFLUSH(3C)