fread man page

fread, fwrite — binary stream input/output


#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);


The function fread() reads nmemb items 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 items of data, each size bytes long, to the stream pointed to by stream, obtaining them from the location given by ptr.

For nonlocking counterparts, see unlocked_stdio(3).

Return Value

On success, fread() and fwrite() return the number of items read or written. This number equals the number of bytes transferred only when size is 1. If an error occurs, or the end of the file is reached, the return value is a short item count (or zero).

fread() does not distinguish between end-of-file and error, and callers must use feof(3) and ferror(3) to determine which occurred.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
fread(), fwrite() Thread safety MT-Safe

Conforming to

POSIX.1-2001, POSIX.1-2008, C89.

See Also

read(2), write(2), feof(3), ferror(3), unlocked_stdio(3)


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Referenced By

cgi_register_parse_cb(3), CURLOPT_WRITEDATA(3), explain(1), explain(3), explain_fread(3), explain_fread_or_die(3), explain_fwrite(3), explain_fwrite_or_die(3), fgetc(3), getline(3), gets(3), getw(3), libraptor(3), perlfunc(1), pmlogger(1), puts(3), read(2), setbuf(3), stdin(3), write(2).

fwrite(3) is an alias of fread(3).

2015-07-23 GNU Linux Programmer's Manual