fread(3) -- Linux man page
NAMEfread, fwrite - binary stream input/output
size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
DESCRIPTIONThe function fread reads nmemb elements of data, each size bytes long, from the stream pointed to by stream, storing them at the location given by ptr.
The function fwrite writes nmemb elements of data, each size bytes long, to the stream pointed to by stream, obtaining them from the location given by ptr.
For non-locking counterparts, see unlocked_stdio(3).
RETURN VALUEfread and fwrite return the number of items successfully read or written (i.e., not the number of characters). If an error occurs, or the end-of-file is reached, the return value is a short item count (or zero).
CONFORMING TOThe functions fread and fwrite conform to ANSI X3.159-1989 (``ANSI C'').
SEE ALSOread(2), write(2), feof(3), ferror(3), unlocked_stdio(3)