.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "FFLUSH" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" fflush 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
fflush \- flush a stream
.SH SYNOPSIS
.LP
\fB#include <stdio.h>
.br
.sp
int fflush(FILE *\fP\fIstream\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
If \fIstream\fP points to an output stream or an update stream in
which the most recent operation was not input,
\fIfflush\fP() shall cause any unwritten data for that stream to be
written to the file,  and the
\fIst_ctime\fP and \fIst_mtime\fP fields of the underlying file shall
be marked for update. 
.LP
If \fIstream\fP is a null pointer, \fIfflush\fP() shall perform this
flushing action on all streams for which the behavior is
defined above.
.SH RETURN VALUE
.LP
Upon successful completion, \fIfflush\fP() shall return 0; otherwise,
it shall set the error indicator for the stream, return
EOF,  
\ and set \fIerrno\fP to indicate the error. 
.SH ERRORS
.LP
The \fIfflush\fP() function shall fail if:
.TP 7
.B EAGAIN
The O_NONBLOCK flag is set for the file descriptor underlying \fIstream\fP
and the process would be delayed in the write
operation. 
.TP 7
.B EBADF
The file descriptor underlying \fIstream\fP is not valid. 
.TP 7
.B EFBIG
An
attempt was made to write a file that exceeds the maximum file size.
.TP 7
.B EFBIG
An attempt was made to write a file that exceeds the process' file
size limit. 
.TP 7
.B EFBIG
The file is a regular file and an attempt was made to write at or
beyond the offset maximum associated with the corresponding
stream. 
.TP 7
.B EINTR
The \fIfflush\fP() function was interrupted by a signal. 
.TP 7
.B 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. This error may also be returned under
implementation-defined conditions. 
.TP 7
.B ENOSPC
There was no free space remaining on the device containing the file.
.TP 7
.B EPIPE
An
attempt is made to write to a pipe or FIFO that is not open for reading
by any process. A SIGPIPE signal shall also be sent to the
thread. 
.sp
.LP
The \fIfflush\fP() function may fail if:
.TP 7
.B ENXIO
A
request was made of a nonexistent device, or the request was outside
the capabilities of the device. 
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Sending Prompts to Standard Output
.LP
The following example uses \fIprintf\fP() calls to print a series
of prompts for
information the user must enter from standard input. The \fIfflush\fP()
calls force the output to standard output. The
\fIfflush\fP() function is used because standard output is usually
buffered and the prompt may not immediately be printed on the
output or terminal. The \fIgets\fP() calls read strings from standard
input and place the
results in variables, for use later in the program.
.sp
.RS
.nf

\fB#include <stdio.h>
\&...
char user[100];
char oldpasswd[100];
char newpasswd[100];
\&...
printf("User name: ");
fflush(stdout);
gets(user);
.sp

printf("Old password: ");
fflush(stdout);
gets(oldpasswd);
.sp

printf("New password: ");
fflush(stdout);
gets(newpasswd);
\&...
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
Data buffered by the system may make determining the validity of the
position of the current file descriptor impractical. Thus,
enforcing the repositioning of the file descriptor after \fIfflush\fP()
on streams open for \fIread\fP() is not mandated by IEEE\ Std\ 1003.1-2001.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIgetrlimit\fP(), \fIulimit\fP(), the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, \fI<stdio.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version 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 .