fread(3p)
NAME
fread - binary input
SYNOPSIS
#include <stdio.h> size_t fread(void *restrict ptr, size_t size, size_t nitems, FILE *restrict stream);
DESCRIPTION
The fread() function shall read into the array pointed to by ptr up to
nitems elements whose size is specified by size in bytes, from the
stream pointed to by stream. For each object, size calls shall be made
to the fgetc() function and the results stored, in the order read, in
an array of unsigned char exactly overlaying the object. The file position indicator for the stream (if defined) shall be advanced by the
number of bytes successfully read. If an error occurs, the resulting
value of the file position indicator for the stream is unspecified. If
a partial element is read, its value is unspecified.
The fread() function may mark the st_atime field of the file associated
with stream for update. The st_atime field shall be marked for update
by the first successful execution of fgetc(), fgets(), fgetwc(),
fgetws(), fread(), fscanf(), getc(), getchar(), gets(), or scanf()
using stream that returns data not supplied by a prior call to ungetc()
or ungetwc().
RETURN VALUE
Upon successful completion, fread() shall return the number of elements
successfully read which is less than nitems only if a read error or
end-of-file is encountered. If size or nitems is 0, fread() shall
return 0 and the contents of the array and the state of the stream
remain unchanged. Otherwise, if a read error occurs, the error indicator for the stream shall be set, and errno shall be set to indicate
the error.
ERRORS
Refer to fgetc() .
The following sections are informative.
EXAMPLES
- Reading from a Stream
- The following example reads a single element from the fp stream into
the array pointed to by buf.
#include <stdio.h>
...
size_t bytes_read;
char buf[100];
FILE *fp;
...
bytes_read = fread(buf, sizeof(buf), 1, fp);
...
APPLICATION USAGE
The ferror() or feof() functions must be used to distinguish between an
error condition and an end-of-file condition.
Because of possible differences in element length and byte ordering,
files written using fwrite() are application-dependent, and possibly
cannot be read using fread() by a different application or by the same
application on a different processor.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
feof() , ferror() , fgetc() , fopen() , getc() , gets() , scanf() , the Base Definitions volume of IEEE Std 1003.1-2001, <stdio.h>
COPYRIGHT
- Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .