seek(+Stream, +Offset)

Stream

Stream handle or alias (atom)

Offset

Integer or the atom end_of_file.

Description

seek/2 seeks to the end of the file when Offset is instantiated to end_of_file.

Only file and string streams are seekable. seek/2 has no effect on the null stream, it always succeeds.

Modes and Determinism

• seek(+, +) is det

Exceptions

(4) instantiation fault

Either Stream or Offset is uninstantiated.

(5) type error

Offset is instantiated, but not to an integer or the atom end_of_file.

(5) type error

Stream is instantiated, but not to an atom or a stream handle.

(6) out of range

Offset is a negative integer or greater than the file length.

(192) illegal stream mode

Stream is not seekable.

(193) illegal stream specification

Stream is an illegal stream specification.

Examples

Success:
      seek(0, null). % does not modify, only succeeds

      ?- open(file1,update,S), write(S,hello),
         seek(S,3), read(S,T), close(S).
      T = lo
      yes.

Error:
      seek( Offset,7).      (Error 4).
      seek("7", 2).         (Error 5).
      seek(7, -1).          (Error 6).
      seek( 0,input).       (Error 192).
      seek(-1, 0).          (Error 193). % does not exist

See Also