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 ele-
ment 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(5) 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(5), standards(5)
SunOS 5.10 24 Jul 2002 fread(3C)