registering class methods as C style callbacks

Mon, 17 Jul 2006 13:35:36 -0400
consider the following problem:

You have a C style library and API that uses callbacks to implement
functionality. Examples of this are X11 API, OpenGL/GLUT...The List goes

The power of virtuals in C++ leads us to want to implement a framework
where those callbacks are simply overriden virtual methods in a derived
class. So...

struct A {
    A() { ::set_timerroutine(timerroutine); }
    ~A() { ::clear_timerroutine(); }
    void timerroutine() { action(); }
    virtual void action()=0;

struct B: public A {
    B(): A() {}
    action() { // do something relevant here }
B myTimerObject;

On the surface we would expect that registering the class method
timerroutine in the constructor for A would cause B::action() to be
invoked but I've not found a way to cast a class method to a generic
function pointer as is expected in C style callbacks.

How can I accomplish this without the extremely ugly overhead of
"referencing static object pointers in a C style timerroutine() that is
not itself a class method?"

The idea/requirement is to have a framework that can exist solely in a
header file and thus serve as a template.


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