#include <stdio.h>

size_t fwrite(const void *restrict ptr, size_t size, size_t nitems,
FILE *restrict stream);


Partially implemented


IEEE Std 1003.1-2017


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.


Refer to fputc.



Known bugs


See Also

  1. Standard library functions
  2. Table of Contents