Virtual overridden function must be implemented in header?

[Halsafar]

Lets say:

class A {
public:
virtual void foo() = 0;
};

class B : public A {
void foo();
}


Now MUST foo()'s implimentation for class 'B' be written in the header?
It seems I have having unresolved external symbols if I try to declare them in a source file.

[twanvl]

It should work fine if you put something like

#include "b.h"

void B::foo() {
}

in a source file.

[Halsafar]

Yah I figure as much, I mean that is obvious. However VC8 is certainly complaining about it. foo() if its implimentation is in a source file I get an "unresolved external symbol". If I move I move the implimentation to the header then it compiles fine. This doesn't seem right... Having worked with Java so long I kinda got some of the finer rules mixed up...

[CornedBee]

Perhaps your project is incorrectly set up, and it doesn't include the separate .cpp file in the linking step?

Or the code that is not an example is actually a template class?