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


fread - binary input


#include <stdio.h>

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


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).


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.


Refer to fgetc(3C).


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);


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.


See attributes(7) for descriptions of the following attributes:

|Interface Stability | Standard |
|MT-Level | MT-Safe |


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)