FWRITE(3P) POSIX Programmer's Manual FWRITE(3P)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.
NAMEfwrite — binary output
size_t fwrite(const void *restrict ptr, size_t size, size_t nitems,
FILE *restrict stream);
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.1‐2008
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 indica‐
tor 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().
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 indi‐
cate the error.
Refer to fputc().
The following sections are informative.
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.
Section 2.5, Standard I/O Streams, ferror(), fopen(), fprintf(),
putc(), puts(), write()
The Base Definitions volume of POSIX.1‐2008, <stdio.h>
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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.ker‐
IEEE/The Open Group 2013 FWRITE(3P)