xref: /illumos-gate/usr/src/man/man3c/fflush.3c (revision a92282e44f968185a6bba094d1e5fece2da819cf)

Sun Microsystems, Inc. gratefully acknowledges The Open Group for
permission to reproduce portions of its copyrighted documentation.
Original documentation from The Open Group can be obtained online at
http://www.opengroup.org/bookstore/.

The Institute of Electrical and Electronics Engineers and The Open
Group, have given us permission to reprint portions of their
documentation.

In the following statement, the phrase ``this text'' refers to portions
of the system documentation.

Portions of this text are reprinted and reproduced in electronic form
in the SunOS Reference Manual, from IEEE Std 1003.1, 2004 Edition,
Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6,
Copyright (C) 2001-2004 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy
between these versions and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html.

This notice shall appear on any product containing this material.

The contents of this file are subject to the terms of the
Common Development and Distribution License (the "License").
You may not use this file except in compliance with the License.

You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
or http://www.opensolaris.org/os/licensing.
See the License for the specific language governing permissions
and limitations under the License.

When distributing Covered Code, include this CDDL HEADER in each
file and include the License file at usr/src/OPENSOLARIS.LICENSE.
If applicable, add the following below this CDDL HEADER, with the
fields enclosed by brackets "[]" replaced with your own identifying
information: Portions Copyright [yyyy] [name of copyright owner]


Copyright (c) 1992, X/Open Company Limited. All Rights Reserved.
Portions Copyright (c) 2002, Sun Microsystems, Inc. All Rights Reserved.

FFLUSH 3C "March 25, 2020"
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(5) for descriptions of the following attributes:
ATTRIBUTE TYPE ATTRIBUTE VALUE
Interface Stability Standard
MT-Level MT-Safe
SEE ALSO
getrlimit(2), ulimit(2), attributes(5), standards(5)