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at(+Stream, ?Pointer)

Succeeds if Pointer is the pointer position of the stream Stream.
+Stream
Integer (stream number) or Atom (reserved or user-defined symbolic stream name).
?Pointer
Integer or variable.

Description

Unifies Pointer with the file position of the file specified by Stream.

Stream can be a symbolic stream name or a physical stream number.

Fail Conditions

Fails if Pointer is not the pointer position of the stream Stream.

Resatisfiable

No.

Exceptions

(4) instantiation fault
Stream is not instantiated.
(5) type error
Pointer is instantiated to a non-integer.
(5) type error
Stream is instantiated to neither an integer nor an atom.
(192) illegal stream mode
Stream is an illegal stream mode.

Examples

Success:
      [eclipse]: open(file1,write,s), at(s, P1),
      > write(s, 1234567890), at(s, P2), close(s).
      P1 = 0
      P2 = 10
      yes.
      [eclipse]: open(file1,update,s), at(s, P1), read(s, T),
      > at(s, P2), close(s).
      P1 = 0
      T = 1234567890
      P2 = 10
      yes.

Error:
      at(Stream, 4).      (Error 4).
      at("3", Pointer).   (Error 5).
      at(7, 4.3).         (Error 5).

See Also

at_eof / 1, seek / 2