FWRITE
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
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.
NAME
fwrite
--- binary output
SYNOPSIS
#include <stdio.h>
size_t fwrite(const void *restrict ptr, size_t size, size_t nitems,
FILE *restrict stream);
DESCRIPTION
The functionality described on this reference page is aligned with the
ISO C standard. Any conflict between the requirements described here and the
ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.
The
fwrite()
function shall write, from the array pointed to by
ptr,
up to
nitems
elements whose size is specified by
size,
to the stream pointed to by
stream.
For each object,
size
calls shall be made to the
fputc()
function, taking the values (in order) from an array of
unsigned char
exactly overlaying the object. The file-position indicator for the
stream (if defined) shall be advanced by the number of bytes
successfully written. If an error occurs, the resulting value of the
file-position indicator for the stream is unspecified.
The last data modification and last file status change timestamps
of the file shall be marked for update between the successful
execution of
fwrite()
and the next successful completion of a call to
fflush()
or
fclose()
on the same stream, or a call to
exit()
or
abort().
RETURN VALUE
The
fwrite()
function shall return the number of elements successfully written,
which may be less than
nitems
if a write error is encountered. If
size
or
nitems
is 0,
fwrite()
shall return 0 and the state of the stream remains unchanged. Otherwise,
if a write error occurs, the error indicator for the stream shall be set,
and
errno
shall be set to indicate the error.
ERRORS
Refer to
fputc().
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
Because of possible differences in element length and byte ordering,
files written using
fwrite()
are application-dependent, and possibly cannot be read using
fread()
by a different application or by the same application on a different
processor.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.5,
Standard I/O Streams,
ferror(),
fopen(),
fprintf(),
putc(),
puts(),
write()
The Base Definitions volume of POSIX.1-2017,
<stdio.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 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 .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .