calling class name in the header file.

Question

Hi,

I just stumbled a c++ code with a calling of a class name in the upper part of the header file for example

class CFoo;
class CBar
{
  ....
};

My question is, what is class CFoo for?

Thanks alot!

Answer 1

This is called a forward declaration. It means that there IS a class named CFoo, that will be defined later in the file (or another include). This is typically used for pointer members in classes, such as:

class CFoo;
class CBar {
    public:
        CFoo* object;
};

It is a hint to the C++ compiler telling it not to freak out that a type name is being used without being defined, even though it hasn't seen the full definition for CFoo yet.

Answer 2

It's called a forward declaration.

http://en.wikipedia.org/wiki/Forward%5Fdeclaration

Answer 3

class CFoo;

Is just a declaration that the class exists; even if you haven't seen the definition yet, you can still play with (CFoo *) or (CFoo &) - that is, pointers and references to CFoo.