Fabien Costantini wrote:
[ Mike Sweet wrote ]
>> IIRC we can't do this since a virtual copy() that calls copy(w,h)
>> will call the wrong copy(w,h) due to a side-effect of how C++ handles
>> such things.
> Here's a little demonstrator of what I am explaining:
>
> #include <stdio.h>
>
> class A {
> public:
> A* copy() { return copy(0,0);}
> virtual A* copy(int,int) {printf("Copy from A\n"); return this;}
> };
>
> class B: public A {
> public:
> virtual A* copy(int,int) {printf("Copy from B\n"); return this;}
> };
>
> int main(int, char**) {
> B b;
> A* a = &b;
> a->copy();
> return 0;
> }
>
> Execute it:
>
> [fab]~/Devl $ g++ test.cxx -o test && ./test
> Copy from B
>
>
> So any non virtual method calling a virtual method will call the right
> derived class method (here B::copy(int, int)
Okay, that works. But what is the side effect, if A::copy() is
virtual? I get the same result. Wrong example?
Albrecht
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