fflush()

Flush the buffers for a stream

Synopsis:

#include <stdio.h>

int fflush( FILE* fp );

Arguments:

fp

NULL, or the stream whose buffers you want to flush.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

If the stream specified by fp is open for output or update, the fflush() function causes any buffered (see setvbuf()) but unwritten data to be written to the file descriptor associated with the stream (see fileno()).

If the file specified by fp is open for input or update, the fflush() function undoes the effect of any preceding ungetc operation on the stream.

If fp is NULL, all open streams are flushed.

Returns:

0 for success, or EOF if an error occurs (errno is set).

Errors:

EAGAIN

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

EBADF

The file descriptor underlying fp isn't valid.

EFBIG

One of the following:

• An attempt was made to write a file that exceeds the maximum file size.
• An attempt was made to write a file that exceeds the process's 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.

EINTR

The fflust() function was interrupted by a signal.

EIO

One of the following:

• 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.
• (QNX Neutrino extension) An I/O error occurred when writing cached data to the underlying media.
• (QNX Neutrino extension) An I/O error occurred when updating metadata on the underlying media.
• (QNX Neutrino extension) The filesystem resides on a removable media device, and the media has been forcibly removed.

ENOSPC

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

ENXIO

A request was made of a nonexistent device, or the request was outside the capabilities of the device.

EPIPE

An attempt was made to write to a pipe or FIFO that wasn't open for reading by any process. A SIGPIPE signal is also sent to the thread.

Examples:

#include <stdio.h>
#include <stdlib.h>

int main( void )
{
    printf( "Press Enter to continue..." );
    fflush( stdout );
    getchar();

    return EXIT_SUCCESS;
}

Classification:

ANSI, POSIX 1003.1

See also:

errno, fgetc(), fgets(), fileno(), flushall(), fopen(), getc(), gets(), setbuf(), setvbuf(), ungetc()