FSEEK(3) BSD Library Functions Manual FSEEK(3)NAME
fgetpos, fseek, fsetpos, ftell, rewind — reposition a stream
fseek(FILE *stream, long offset, int whence);
fgetpos(FILE *stream, fpos_t *pos);
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 to:
(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 stor‐
ing the current value of the file offset into or from the object refer‐
enced 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 reposi‐
tion a text stream.
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 indicate 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 con‐
form to ANSI X3.159-1989 (“ANSI C89”).
BSD June 4, 1993 BSD