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get_stream_info(+Stream, ?Attr, -Value)

Succeeds if the attribute Attr of the open stream Stream has the value Value.
Stream handle or alias (atom)
Atom or variable.
Variable, atom, string, integer or handle.


Used to retrieve information associated to an open stream. The available attributes and their meanings are:

    Attr            Value         Description

    aliases         integer       current number of symbolic names

    compress        on, off       a hint for output operations (e.g.
                                  write_exdr/2) to use a more compact
                                  output format (output streams only).
                                  Default: on (file,pipe,socket) or off.

    connection      atom          identification of the connected
                                  socket - file name for unix sockets,
                                  host name for internet ones

    delete_file     off,          delete an opened file automatically when:
                    when_lost,    - its stream handle becomes inaccessible
                    when_closed   - the stream is closed in any way

    device          file, null,   the device behind the stream
                    pipe, queue,
                    socket, tty,

    encoding        octet,        character encoding used by this stream

    end_of_line     lf, crlf      which end-of-line sequence to write
                                  (output streams only)

    end_of_stream   at,not,past   indicates whether the stream is currently
                                  positioned at (or past) the end-of-file

    eof_action      eof_code,     how to react to end-of-file
                    error,        (input streams only)

    event           atom or       event on writing to empty stream
                    event handle  (see open/4)

    fd              integer       the associated OS file descriptor

    flush           flush,        explicit or implicit flushing
                    end_of_line   (output streams only)

    handle          stream handle a garbage-collectable handle to the stream
                                  (see also get_stream/2)

    input           true, false   this is an input stream (ISO)

    last_written    integer       character code of last written character
                                  (output streams only)

    line            integer       current line number
                                  (input streams only)

    mode            read, write,  the stream's direction

    name            atom or       associated filename, or contents
                    string        (in case of a string or queue), or
                                  pseudo file name (user, error, null)

    macro_expansion on, off       expand term macros (input streams only)

    offset          integer       current position in the
                                  stream, as given by at/2

    output          true, false   this is an input stream (ISO)

    output_options  list          default output options for all term
                                  output on this stream. The list
                                  format is as in write_term/2,3.

    physical_stream integer       associated stream number
                                  (DEPRECATED: if this number is retrieved,
                                  the system will no longer be able to close
                                  the stream automatically when unused)

    port            integer       port number associated with an
                                  internet socket

    prompt          string        prompt string (input streams only)

    prompt_stream   handle        output stream for the prompt
                                  (input streams only)

    reposition      true, false   the stream can be repositioned (seek/2)

    sigio           on            SIGIO signals enabled (UNIX only)

    system_use      on, off       a system stream is currently
                                  redirected to this stream

    usable          on, off       if the stream can currently be used:
                                  flushing or reading the empty stream
                                  may not be properly handled if `off'.

    yield           on, off       yield on end-of-file (see open/4)

Modes and Determinism

Fail Conditions

Fails if the requested attribute is not available for this stream


(4) instantiation fault
Stream is not instantiated.
(5) type error
Stream is neither an atom nor a handle.
(5) type error
Attr is instantiated, but not to an atom.
(5) type error
Value is instantiated, but not to an atom, string, integer or handle.
(6) out of range
Attr is an atom, but not a valid attribute name.
(193) illegal stream specification
Stream does not denote an open stream.


    ?- get_stream_info(input,X,Y), writeln(X is Y), fail.
    name is user
    aliases is 2
    system_use is on
    line is 1
    offset is 0
    prompt is
    prompt_stream is $&(stream,1)
    fd is 0
    reprompt_only is off
    device is tty
    mode is read
    usable is on
    macro_expansion is on
    handle is $&(stream,0)
    No (0.00s cpu)

    ?- get_stream_info(toplevel_input, prompt, P).
    P = "\t"
    Yes (0.00s cpu)

    get_stream_info(output, prompt, P).
    get_stream_info(output, system_use, off).

    get_stream_info(X, Y, Z).                      (Error 4)
    get_stream_info(file(f), Y, Z).                (Error 5)
    get_stream_info(output, 7, X).                 (Error 5)
    get_stream_info(output, offset, 8.5).          (Error 5)
    get_stream_info(output, length, Z).            (Error 6)
    get_stream_info(nostream, Y, Z).               (Error 193)

See Also

set_stream_property / 3, open / 3, open / 4, current_stream / 1, get_stream_info / 3, get_stream / 2, at / 2, write_term / 2, write_term / 3