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From: dog@cbnewsl.ATT.COM (edward.n.schiebel)
Newsgroups: comp.lang.c++,comp.windows.x
Subject: Re: using X11 with C++ callbacks
Message-ID: <2374@cbnewsl.ATT.COM>
Date: 20 Oct 89 11:47:04 GMT
References: <640@sunquest.UUCP>
Organization: AT&T Bell Laboratories
Lines: 36

From article <640@sunquest.UUCP>, by francis@sunquest.UUCP (Francis Sullivan):
> I would like to be able to use C++ callbacks in X11.  Since this is not
> supported, I'm trying to come up with a simple method to simulate this.
> For now I just write a C wrapper that calls the correct C++ routine, but
> I get the feeling that there is an easier way.
[...code deleted...]

I have implemented one solution in SunView, but it seems to be the same 
problem.

First, I have an abstract base class

class dispatchable {
public:
	virtual int doit() = 0;
};

the application derives specific classes from this one to do the
program's stuff.

Now, each Button, Menu_item etc. is given a dispatchable* (either through
some client data mechanism or by creating a class Button which 
encapsulates the X/SunView implementation).  When a button is pressed,
grab its dispatchable* and call doit().

As an aside, I have noticed
to get anything like this to work well takes a lot more time up front
providing support classes etc., but in the end, the application is
so much easier to write.

Hope this is useful, it has worked for me.

	Ed Schiebel
	AT&T Bell Laboratories
	dog@vila.att.com
	201-386-3416