FWRITE(P) POSIX Programmer's Manual FWRITE(P)
fwrite - binary output
size_t fwrite(const void *restrict ptr, size_t size, size_t nitems,
FILE *restrict stream);
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 unspec-
The st_ctime and st_mtime fields of the file shall be marked for update between the suc-
cessful 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
indicate 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 differ-
ent application or by the same application on a different processor.
ferror() , fopen() , printf() , putc() , puts() , write() , the Base Definitions volume of
IEEE Std 1003.1-2001, <stdio.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 FWRITE(P)