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From: keffer@blake.acs.washington.edu (Thomas Keffer)
Newsgroups: comp.lang.c++,comp.windows.x
Subject: Re: using X11 with C++ callbacks
Message-ID: <4126@blake.acs.washington.edu>
Date: 20 Oct 89 19:01:20 GMT
References: <640@sunquest.UUCP> <1948@bacchus.dec.com>
Reply-To: keffer@blake.acs.washington.edu (Thomas Keffer)
Organization: University of Washington, Seattle
Lines: 33

In article <1948@bacchus.dec.com> haynes@gnome5.pa.dec.com (Charles Haynes) writes:
>Use the "this" pointer as the client data in the X callback. Write a
>generic wrapper function that takes a class pointer, and a pointer to a
>method, and calls that method in that class. The method should have no
>other args. Use the wrapper as the callback and the class as the client data.
>

This is essentially the strategy that I have followed with SunView
except that I make the callback routine a static member function of
the appropriate class (in my case, I have defined a ``Panel'' class
that manages a window).  The callback routine looks something like:

void
Panel::someButtonCallBack(Panel_item p, int value, Event *e)
{
	PanelClient* this_client = panel_get(p, CLIENT_DATA);
	this_client->memberFunctionYouWantToCall(value);
}

Or something like that.  Here, PanelClient is the object being
maniupulated on behalf of the window. The advantage of using a
static member function is to further encapsulation while giving you
access to the appropriate member functions and variables.

An example is available via anonymous ftp from
sperm.ocean.washington.edu in file ~ftp/pub/spinup.tar.Z

-Tom Keffer

Rogue Wave
P.O. Box 85341
Seattle Wa 98145-1341
(206) 523-5831