get_stream(+StreamId, ?Stream)

StreamId

Stream alias (atom), or handle

Stream

Variable, stream handle or alias (atom)

Description

StreamId is an existing symbolic stream alias or a stream handle. If Stream is a variable, it will get bound to a stream handle corresponding to StreamId. If Stream is a symbolic stream alias or a handle, then the predicate succeeds iff StreamId and Stream denote the same stream.

The predefined symbolic system stream names are:

input, output, error, warning_output, log_output, stdin, stdout, stderr, null

Modes and Determinism

• get_stream(+, -) is det
• get_stream(+, +) is semidet

Fail Conditions

Exceptions

(4) instantiation fault

One or both of StreamId and Stream is not instantiated.

(5) type error

Stream is neither an atom, a stream handle nor a variable.

(5) type error

StreamId is neither an atom nor a stream handle.

(193) illegal stream specification

StreamId is an illegal stream specification.

Examples

Success:
      ?- get_stream(input,S).
      S = $&(stream,0)
      Yes (0.00s cpu)

      ?- set_stream(a,input), get_stream(input,a), get_stream(a,input).
      Yes (0.00s cpu)

Fail:
      set_stream(b,input), get_stream(b,output).

Error:
      get_stream(Id, S).      (Error 4).
      get_stream(1.0,S).      (Error 5).
      get_stream(3, S).       (Error 5).
      get_stream(blah,S).     (Error 193). % does not exist

See Also