fwrite(3p) — Linux manual page


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.1‐2017 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         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

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.1‐2017, stdio.h(0p)

COPYRIGHT         top

       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(3P)

Pages that refer to this page: stdio.h(0p)