FREAD(3) | Library Functions Manual | FREAD(3) |
fread
, fwrite
—
#include <stdio.h>
size_t
fread
(void
* restrict ptr, size_t
size, size_t nmemb,
FILE * restrict
stream);
size_t
fwrite
(const
void * restrict ptr,
size_t size,
size_t nmemb,
FILE * restrict
stream);
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 ptr.
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.
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 (or zero).
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.
fread
() and
fwrite
() conform to ANSI X3.159-1989
(“ANSI C89”).
September 11, 2011 | NetBSD 9.0 |