mirror of https://github.com/mkerrisk/man-pages
151 lines
4.2 KiB
Plaintext
151 lines
4.2 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "FFLUSH" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" fflush
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.SH NAME
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fflush \- flush a stream
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.SH SYNOPSIS
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.LP
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\fB#include <stdio.h>
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.br
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.sp
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int fflush(FILE *\fP\fIstream\fP\fB);
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.br
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\fP
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.SH DESCRIPTION
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.LP
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If \fIstream\fP points to an output stream or an update stream in
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which the most recent operation was not input,
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\fIfflush\fP() shall cause any unwritten data for that stream to be
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written to the file, \ and the
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\fIst_ctime\fP and \fIst_mtime\fP fields of the underlying file shall
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be marked for update.
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.LP
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If \fIstream\fP is a null pointer, \fIfflush\fP() shall perform this
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flushing action on all streams for which the behavior is
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defined above.
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.SH RETURN VALUE
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.LP
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Upon successful completion, \fIfflush\fP() shall return 0; otherwise,
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it shall set the error indicator for the stream, return
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EOF,
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\ and set \fIerrno\fP to indicate the error.
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.SH ERRORS
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.LP
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The \fIfflush\fP() function shall fail if:
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.TP 7
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.B EAGAIN
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The O_NONBLOCK flag is set for the file descriptor underlying \fIstream\fP
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and the process would be delayed in the write
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operation.
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.TP 7
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.B EBADF
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The file descriptor underlying \fIstream\fP is not valid.
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.TP 7
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.B EFBIG
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An
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attempt was made to write a file that exceeds the maximum file size.
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.TP 7
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.B EFBIG
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An attempt was made to write a file that exceeds the process' file
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size limit.
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.TP 7
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.B EFBIG
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The file is a regular file and an attempt was made to write at or
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beyond the offset maximum associated with the corresponding
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stream.
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.TP 7
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.B EINTR
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The \fIfflush\fP() function was interrupted by a signal.
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.TP 7
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.B EIO
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The process is a member of a background process group attempting to
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write to its controlling terminal, TOSTOP is set, the process
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is neither ignoring nor blocking SIGTTOU, and the process group of
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the process is orphaned. This error may also be returned under
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implementation-defined conditions.
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.TP 7
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.B ENOSPC
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There was no free space remaining on the device containing the file.
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.TP 7
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.B EPIPE
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An
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attempt is made to write to a pipe or FIFO that is not open for reading
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by any process. A SIGPIPE signal shall also be sent to the
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thread.
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.sp
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.LP
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The \fIfflush\fP() function may fail if:
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.TP 7
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.B ENXIO
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A
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request was made of a nonexistent device, or the request was outside
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the capabilities of the device.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.SS Sending Prompts to Standard Output
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.LP
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The following example uses \fIprintf\fP() calls to print a series
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of prompts for
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information the user must enter from standard input. The \fIfflush\fP()
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calls force the output to standard output. The
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\fIfflush\fP() function is used because standard output is usually
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buffered and the prompt may not immediately be printed on the
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output or terminal. The \fIgets\fP() calls read strings from standard
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input and place the
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results in variables, for use later in the program.
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.sp
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.RS
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.nf
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\fB#include <stdio.h>
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\&...
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char user[100];
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char oldpasswd[100];
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char newpasswd[100];
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\&...
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printf("User name: ");
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fflush(stdout);
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gets(user);
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.sp
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printf("Old password: ");
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fflush(stdout);
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gets(oldpasswd);
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.sp
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printf("New password: ");
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fflush(stdout);
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gets(newpasswd);
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\&...
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\fP
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.fi
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.RE
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.SH APPLICATION USAGE
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.LP
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None.
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.SH RATIONALE
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.LP
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Data buffered by the system may make determining the validity of the
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position of the current file descriptor impractical. Thus,
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enforcing the repositioning of the file descriptor after \fIfflush\fP()
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on streams open for \fIread\fP() is not mandated by IEEE\ Std\ 1003.1-2001.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIgetrlimit\fP() , \fIulimit\fP() , the Base Definitions volume of
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IEEE\ Std\ 1003.1-2001, \fI<stdio.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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