Objects and pointers to member functions.

[Marklar]

I am trying to achieve something like the following ....

class A {
void functionA1(void (*pt2FuncB1)()) {
pt2FuncB1();
}
}

class B {
A objA;

void functionB1() {
// Do Something
}

void functionB2() {
objA.function(&functionB1)
}

}

Where an object passes a pointer to a member function to a member object function. Is there a way to make this possible with minimal changes to class A? Class A and B do not share a namespace either.

[newb16]

something like in p33.5 -
http://www.parashift.com/c++-faq-lit...o-members.html
Or give up and use static member.

[weaknessforcats]

You can't pass pointers to member functions. You see, the compiler supplies the address of the object as the first argument when the member functi is called.

By calling it by pointer somewhere else, the address of the object has been lost.

There should be no scenario where you need to do this. I would ask you to explain your design in greater detail. I expect there is another solution.

[Marklar]

Here is a description of what I am trying to do.

Well I have built a system for rendering an opengl scene but I want the the library I have built to be able to be used with no alterations to my code and minimal changes to any opengl application which may use it in future. In my planned design the user creates an instance of the rendering system class in their application simply passing the a pointer to the applications normal rendering function, then the rendering callback calls the rendering function of the rendering system instead of the usual render function.

Thanks for the responses

[Marklar]

I thought this should be possible given that the instance of my class is also a member of the object whose function I am trying to access.

I am thinking now more along the lines that making the users application a child class of my class might be the required solution.

[Savage]

I thought this should be possible given that the instance of my class is also a member of the object whose function I am trying to access.

I am thinking now more along the lines that making the users application a child class of my class might be the required solution.

Don't use callbacks.It's procedural way.
C++ supports OOP,so why not make a abstract class.
User would derive and implement pure virtual functions and then pass it to your rendering system which will in turn call derived class functions to render stuff.

[Marklar]

Don't use callbacks.It's procedural way.
C++ supports OOP,so why not make a abstract class.
User would derive and implement pure virtual functions and then pass it to your rendering system which will in turn call derived class functions to render stuff.

This would work but doesnt exactly make it easy to implement into existing OpenGL application, and seems like overkill given that all I need to call is the render routine.

I think I can use 33.5 from the C++ faq I shall have a play and let you all know.

[Marklar]

Thanks for the help, I have ended up using something like what savage suggested it is still a little messy so I am going to try simplifying the implementation for users a bit more. Not the one liner I was hoping for but it does the trick for now ... thanks again. Kinda frustrating and odd in some ways.

[weaknessforcats]

Read this: http://bytes.com/forum/thread793836.html.

And then read this: http://bytes.com/forum/thread674645.html.

Having got that far, research using an Abstract Factory to create your rendering system instance.

If you think it's kinda messy, then it's probably worse than you think.