Question

In A.hpp file I have a structure, which has a pointer of B class

struct state
{
    B  *b;
};

In A.hpp file, I added a forward declaration and I included B.hpp file in A.cpp file

//A.hpp
class B

In B.hpp file, a function uses the state, which declared in A.hpp as an argument on the function.

bool function_in_b(state *s)

I also added a forward declaration of A in B.hpp file and I added the header file of A, A.hpp in B.cpp file.

//B.hpp
class A

All header files have a header guard. If I try to compile, it won’t find ‘state’ declared in A.hpp. Thus, it won’t find the matching function and complains the candidates are

bool function_in_b(int *) 

How do I fix this problem?

Answer 1

In B.hpp, you say you forward-declared A, but not state – so when it first sees function_in_b(state *s) it doesn’t know what state is. By the time you include A.hpp in B.cpp it’s too late. You need to forward declare state in B.hpp, i.e.

struct state;

bool function_in_b(state *s);