Tribblix: manual page: fread.3c

FREAD(3C) Standard C Library Functions FREAD(3C)

NAME

fread - binary input

SYNOPSIS

#include <stdio.h>

size_t fread(void *ptr, size_t size, size_t nitems, FILE *stream);

DESCRIPTION

The fread() function reads 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 are made to
the fgetc(3C) 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) is 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 will be marked
for update by the first successful execution of fgetc(3C), fgets(3C),
fgetwc(3C), fgetws(3C), fread(), fscanf(3C), getc(3C), getchar(3C),
gets(3C), or scanf(3C) using stream that returns data not supplied by
a prior call to ungetc(3C) or ungetwc(3C).

RETURN VALUES

Upon successful completion, fread() returns 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() returns 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 is set and errno is set to indicate the error.

ERRORS

Refer to fgetc(3C).

EXAMPLES

Example 1: 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);
...

USAGE

The ferror() or feof() functions must be used to distinguish between
an error condition and end-of-file condition. See ferror(3C).

Because of possible differences in element length and byte ordering,
files written using fwrite(3C) are application-dependent, and
possibly cannot be read using fread() by a different application or
by the same application on a different processor.

ATTRIBUTES