4.24 fread, fread_unlocked—read array elements from a file

Synopsis

#include <stdio.h>
size_t fread(void *restrict buf, size_t size, size_t count,
    FILE *restrict fp);

#define _BSD_SOURCE
#include <stdio.h>
size_t fread_unlocked(void *restrict buf, size_t size, size_t count,
    FILE *restrict fp);

#include <stdio.h>
size_t _fread_r(struct _reent *ptr, void *restrict buf,
    size_t size, size_t count, FILE *restrict fp);

#include <stdio.h>
size_t _fread_unlocked_r(struct _reent *ptr, void *restrict buf,
    size_t size, size_t count, FILE *restrict fp);

Description
fread attempts to copy, from the file or stream identified by fp, count elements (each of size size) into memory, starting at buf. fread may copy fewer elements than count if an error, or end of file, intervenes.

fread also advances the file position indicator (if any) for fp by the number of characters actually read.

fread_unlocked is a non-thread-safe version of fread. fread_unlocked may only safely be used within a scope protected by flockfile() (or ftrylockfile()) and funlockfile(). This function may safely be used in a multi-threaded program if and only if they are called while the invoking thread owns the (FILE *) object, as is the case after a successful call to the flockfile() or ftrylockfile() functions. If threads are disabled, then fread_unlocked is equivalent to fread.

_fread_r and _fread_unlocked_r are simply reentrant versions of the above that take an additional reentrant structure pointer argument: ptr.

Returns
The result of fread is the number of elements it succeeded in reading.

Portability
ANSI C requires fread.

fread_unlocked is a BSD extension also provided by GNU libc.

Supporting OS subroutines required: close, fstat, isatty, lseek, read, sbrk, write.