FREAD(P) POSIX Programmer's Manual FREAD(P)
fread - binary input
size_t fread(void *restrict ptr, size_t size, size_t nitems,
FILE *restrict stream);
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 success-
fully 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
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.
Refer to fgetc() .
The following sections are informative.
Reading from a Stream
The following example reads a single element from the fp stream into the array pointed to
bytes_read = fread(buf, sizeof(buf), 1, fp);
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 differ-
ent application or by the same application on a different processor.
feof() , ferror() , fgetc() , fopen() , getc() , gets() , scanf() , the Base Definitions
volume of IEEE Std 1003.1-2001, <stdio.h>
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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 FREAD(P)