What about this?

class Class1{ //dialog class
int m_1;

void setm1(int m);
}

class Class2{
HWND tbd;

}


Class1::Class1(){
Class2 c2;
c2.tbd = m_hWnd;
}

Class2::Class2(){
tbd->setm1 - //why wont this work???
}

All I want to do is add to a listbox on a dialog from a child class of the dialog...

not certain what you're trying to do, but the HWND handle is just for passing to api functions, declare tbd as Class1* maybe?

I tried that... All I want to do is call a dialog function that will add a string to the list box.

you'd need to pass an argument as well, that function name wont do anything

I did pass an argument. The compiler doesn't understand the relationship between the pointer and the function..

tbd->setm1(2)

gives a compiler error of:

C2227 left of -> must point to class/struct/union.

I did include the header file in the code, too.

The compiler error says it all: HWND is not a struct/union/class pointer