size_t fwrite(const void *ptr, size_t size, size_t nitems, FILE *stream);
The fwrite() function writes, 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 are
made to the fputc(3C) 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) is 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 st_ctime and st_mtime fields of the file will be
marked for update between the successful execution of fwrite() and
the next successful completion of a call to fflush(3C) or
fclose(3C) on the same stream or a call to exit(2) or
When using the fwrite() function on a stream that was
created with open_wmemstream(3C), there are additional constraints on
the binary data that can be written due to the nature of the stream. Please
see open_wmemstream(3C) for additional information.
The fwrite() function returns the number of elements successfully
written, which might be less than nitems if a write error is
encountered. If size or nitems is 0, fwrite() returns 0
and the state of the stream remains unchanged. Otherwise, if a write error
occurs, the error indicator for the stream is set and errno is set to
indicate the error.
Because of possible differences in element length and byte ordering, files
written using fwrite() are application-dependent, and possibly cannot
be read using fread(3C) by a different application or by the same
application on a different processor.
See attributes(7) for descriptions of the following attributes:
write(2), fclose(3C), ferror(3C), fopen(3C),
fread(3C), getc(3C), gets(3C),
open_wmemstream(3C), printf(3C), putc(3C),
puts(3C), attributes(7), standards(7)