FWRITE(3C) Standard C Library Functions FWRITE(3C)


fwrite - binary output


#include <stdio.h>

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 abort(3C).

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.


Refer to fputc(3C).


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:

|Interface Stability | Standard |
|MT-Level | MT-Safe |


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)

March 25, 2020 FWRITE(3C)