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 .