Question

I have a base interface class:

class A
{
public:
    ITask(){}
    virtual bool Start()=0;
    virtual void Update()=0;
    virtual void Stop()=0;
};

I now have 2 other classes, that inherit from this

#include "A.h"
#include "C.h"
class B: public A
{
public:
    bool Start(){} 
    void Update()
    {
        c.Start();
    } 
    void Stop(){}

    static bool m_run;

    static void SetRun(bool run)
    {
        m_run = run;
    }
private:
    C c;
};

lastly I have a 3rd class:

#include "A.h"
#include "B.h"
class C : public A
{
public:
    bool Start()
    {
        B::SetRun(false); // cant do this
        B::m_run = false; // or this
    }
    void Update()
    {

    }
    void Stop()
    {

    }
}

I have shaved down some of the code, for simplicity.

I dont understand why I cant access the static var in B. Do I need to make it a pointer or a ref?

I get 2 errors:

error C2653: 'B' : is not a class or namespace name
error C3861: 'm_run': identifier not found

Answer 1

Although you don’t show it, I’m assuming that B.h includes C.h; otherwise the line C c; won’t compile. This causes a circular dependency in the header files: B.h must be included before C.h, which must be included before B.h, which is impossible.

The easiest solution is to move the body of C::Start out of the definition of C, so that C.h does not need to include B.h. The function definition can go into a source file, or a separate header if you want to keep it inline.

Alternatively, you could modify B to contain a std::unique_ptr<C> rather than an instance of C, and implement a constructor (in a source file, or a separate header) that initialises it with new C. Then B.h only needs to forward declare class C; rather than including C.h.

A better solution, if possible, would be to rethink the relationships between the classes so that there isn’t a circular dependency.

(UPDATE: while I was writing this answer, the question changed to show that B.h does indeed include C.h as I guessed.)