FSEEK(3) Linux Programmer's Manual FSEEK(3)
fgetpos, fseek, fsetpos, ftell, rewind - reposition a stream
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);
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 indi-
cator 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
(void)fseek(stream, 0L, SEEK_SET)
except that the error indicator for the stream is also cleared (see
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
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 the global variable errno is set to indi-
cate the error.
EBADF The stream specified is not a seekable stream.
EINVAL The whence argument to fseek was not SEEK_SET, SEEK_END, or
The function 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).
The fgetpos, fsetpos, fseek, ftell, and rewind functions conform to
ANSI X3.159-1989 (``ANSI C'').
BSD MANPAGE 1993-11-29 FSEEK(3)