FWRITE(3)                  POSIX Programmer's Manual                 FWRITE(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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 .



IEEE/The Open Group                  2017                            FWRITE(3)
