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From: XITIJSCH@DDATHD21.BITNET
Newsgroups: comp.windows.x
Subject: Re: C++ and X: Member-Functions as Callbacks
Message-ID: <9103111132.AA29489@expo.lcs.mit.edu>
Date: 11 Mar 91 15:13:55 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 40
X-Unparsable-Date: Mon, 11 Mar 91 10:37:00 MEZ

Try the following (I assume you use an ANSI C preprocessor):


--- This goes into a general header file:

#define use_as_callback(Class, foo) \
        void foo##_dispatch(Widget w, Class *object, caddr_t call_data) \
        { \
                object->foo(w, 0, call_data); \
        }

#define Cpp_callback(foo) foo##_dispatch



--- This is your C++ code:

class Name_of_class {
        ...
        void do_it(Widget w, caddr_t client_data, caddr_t call_data);
        ...
};

use_as_callback(Name_of_class, do_it);

..

        Name_of_class object;
        ...
        XtAddCallback(w, Cpp_callback(do_it), &object);

or, if you use Motif, you will register Cpp_callback(do_it) and pass &object
via an UIL identifier, etc.

There remains a problem with this approach: You cannot pass client_data
-- but perhaps you may attach it as userdata to the widget.

--
Joachim Schrod                          <xitijsch@ddathd21.bitnet>
Technical University of Darmstadt