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
See
attributes(7) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+
SEE ALSO
read(2),
fclose(3C),
ferror(3C),
fopen(3C),
getc(3C),
gets(3C),
printf(3C),
putc(3C),
puts(3C),
attributes(7),
standards(7) July 24, 2002
FREAD(3C)