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FREAD(3) Library Functions Manual FREAD(3)

NAME

fread, fwritebinary stream input/output

SYNOPSIS

#include <stdio.h>
size_t
fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
size_t
fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream);

DESCRIPTION

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 ptr.

RETURN VALUES

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, fread() and fwrite() return 0 with no change made to the stream. If the product of size and nmemb results in integer overflow, 0 is returned and errno is set to EOVERFLOW. 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.

SEE ALSO

read(2), write(2)

STANDARDS

The functions fread() and fwrite() conform to ANSI X3.159-1989 (“ANSI C89”).

HISTORY

The functions fread() and fwrite() first appeared in Version 7 AT&T UNIX.
March 12, 2015 OpenBSD-current