FREAD(3) Library Functions Manual FREAD(3)
fread, fwrite -- binary stream input/output
Standard C Library (libc, -lc)
fread(void * restrict ptr, size_t size, size_t nmemb, FILE * restrict
fwrite(const void * restrict ptr, size_t size, size_t nmemb, FILE *
The function fread() reads nmemb objects, each size bytes long, from the
stream pointed to by stream, storing them at the location given by ptr.
The function fwrite() writes nmemb objects, each size bytes long, to the
stream pointed to by stream, obtaining them from the location given by
Mixing fread() and fwrite() calls without setting the file position
explicitly using fsetpos(3) between read and write or write and read
operations will lead to unexpected results because of buffering the file
pointer not being set to the expected position after each operation
completes. This behavior is allowed by ANSI C for efficiency and it will
not be changed.
The functions fread() and fwrite() advance the file position indicator
for the stream by the number of bytes read or written. They return the
number of objects read or written. If size or nmemb is 0, the functions
return 0 and the state of stream remains unchanged. If an error occurs,
or the end-of-file is reached, the return value is a short object count
The function fread() does not distinguish between end-of-file and error,
and callers must use feof(3) and ferror(3) to determine which occurred.
The function fwrite() returns a value less than nmemb only if a write
error has occurred.
The functions fread() and fwrite() conform to ANSI X3.159-1989
NetBSD 6.1.5 September 11, 2011 NetBSD 6.1.5