stream_truncate(+Stream)

Stream

Stream handle or alias (atom)

Description

This operation only makes sense on file-streams and string streams which are open for writing (or updating). On all other types of streams, the predicate silently succeeds.

Files will be physically truncated, i.e. their size is trimmed and extra disk space returned to the operating system. String streams will free any unnecessary buffer memory.

Note: When opening an existing file for writing (not updating), the file is automatically truncated to size zero (see open/3,4).

Modes and Determinism

• stream_truncate(+) is det

Exceptions

(4) instantiation fault

Stream is not instantiated.

(5) type error

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

(192) illegal stream mode

Stream is not open in write mode.

Examples

        ?- open(string("hellothere"), update, s).
        Yes (0.00s cpu)

        ?- seek(s, 5).
        Yes (0.00s cpu)

        ?- at_eof(s).
        No (0.00s cpu)

        ?- stream_truncate(s).
        Yes (0.00s cpu)

        ?- at_eof(s).
        Yes (0.00s cpu)

        ?- seek(s,0).
        Yes (0.00s cpu)

        ?- read_string(s, end_of_file, _, S).
        S = "hello"
        Yes (0.00s cpu)

See Also