add-stream-instance-flags

Arguments: stream &rest flag-names

This macro adds (via logior) instance flags to or zeroes instance flags out of the standard-instance object that is the stream. Note that this flags field has no correlation to a flags slot in the stream. You may inspect a stream in raw mode to see the instance-flags (see inspector.htm).

The behavior depends on the first of the flag-names arguments. If it is a keyword specifying a valid instance flag, then it and all the remaining keyword-named instance flags are added. But if the first of the flag-names arguments is a list of flag names, then those are zeroed out before the remaining flag-names (if any) are added. For example, the form

(add-stream-instance-flags stream (:gray :dual :string) :simple)

first ensures that the :gray, :dual, and :string bits are zero, before ensuring that the :simple bit is set. This is done without modifiying the :input or :output bits. On the other hand, this form

(add-stream-instance-flags stream :string :simple)

simply ensures the :string and :simple flags are set.

Valid instance flags are placed into the following groups:

• Direct stream subclass (select exactly one): :gray (identifies a Gray or fundamental-stream) or :simple (identifies a simple-stream). A stream instance that has neither bit set is not considered a stream.
• Open-ness (select one, both, or none): :input (stream may perform input operations); :output (stream may perform output operations). A stream instance that has neither bit set is not considered an open stream.
• Direct simple-stream subclass (select zero or one): :dual (stream is a dual-channel stream); :string (stream is a string-stream). A stream with neither bit set is considered a single-channel stream

You must load the :iodefs module to use this macro. Do that by evaluating (require :iodefs). (It is not an error to evaluate that form if the module is already loaded.) This macro is intended for implementing device-level functionality and should not be used except for that purpose. See Simple-stream Description in streams.htm for a description of the device-level.

See streams.htm for information on the simple-streams implementation in Allegro CL.

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This page was not revised from the 8.2 page.
Created 2012.5.30.