From:
http://linux.die.net/man/3/fseek
Name
fgetpos, fseek, fsetpos, ftell, rewind - reposition a stream
Synopsis
#include <stdio.h>
int fseek(FILE *stream, long offset, int
whence);
long ftell(FILE *stream);
void rewind(FILE *stream);
int fgetpos(FILE *stream, fpos_t *pos);
int fsetpos(FILE *stream, fpos_t *pos);
Description
The fseek() function sets the file position indicator for the stream pointed to by
stream. The new position, measured in bytes, is obtained by adding offset bytes to the position specified by
whence. If whence is set to SEEK_SET,
SEEK_CUR, or SEEK_END, the offset is relative to the start of the file, the current position indicator, or end-of-file, respectively. A successful call to the
fseek() function clears the end-of-file indicator for the stream and undoes any effects of the
ungetc(3) function on the same stream.
The ftell() function obtains the current value of the file position indicator for the stream pointed to by
stream.
The rewind() function sets the file position indicator for the stream pointed to by
stream to the beginning of the file. It is equivalent to:
(void) fseek(stream, 0L, SEEK_SET)
except that the error indicator for the stream is also cleared (see clearerr(3)).
The fgetpos() and fsetpos() functions are alternate interfaces equivalent to
ftell() and fseek() (with whence set to
SEEK_SET), setting and storing the current value of the file offset into or from the object referenced by
pos. On some non-UNIX systems, an fpos_t object may be a complex object and these routines may be the only way to portably reposition a text stream.
Return Value
The rewind() function returns no value. Upon successful completion,
fgetpos(), fseek(), fsetpos() return 0, and
ftell() returns the current offset. Otherwise, -1 is returned and
errno is set to indicate the error.
Errors
- EBADF
- The stream specified is not a seekable stream.
- EINVAL
- The whence argument to fseek() was not SEEK_SET,
SEEK_END, or SEEK_CUR.
The functions fgetpos(), fseek(), fsetpos(), and
ftell() may also fail and set errno for any of the errors specified for the routines
fflush(3),
fstat(2),
lseek(2), and
malloc(3).