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

PROLOG         top

       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         top

       fwrite — binary output

SYNOPSIS         top

       #include <stdio.h>

       size_t fwrite(const void *restrict ptr, size_t size, size_t nitems,
           FILE *restrict stream);

DESCRIPTION         top

       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
       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         top

       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         top

       Refer to fputc(3p).

       The following sections are informative.

EXAMPLES         top



       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         top




SEE ALSO         top

       Section 2.5, Standard I/O Streams, ferror(3p), fopen(3p),
       fprintf(3p), putc(3p), puts(3p), write(3p)

       The Base Definitions volume of POSIX.1‐2008, stdio.h(0p)

COPYRIGHT         top

       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 Electrical 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 .

       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 .

IEEE/The Open Group                 2013                          FWRITE(3P)