Question

I have a class, its object will be used by another class as following

class A
{
public:
    void F() {...}
};

class B
{
public:
    void G() { m_a->F(); ...} // use A's function

private:
    A* m_a;
};

Thus it is wrong to call B::G() before the assignment of pointer m_a. Is this acceptable design? Or there is a better way to do it.

The question comes from developing a GUI application. I have a window under the main window to show some basic information of current operation, such as what is happening, how long does it take, and so on. I put this window as a singleton for easy access by the operations which may scatter anywhere, and find the code crashes when closing the GUI application. The crash is due to the window is deleted after the deletion of GUI application (such as qApp in Qt). I then just put a reference pointer of the window in the singleton. And when the window is constructed, I set the reference pointer. The deletion of the window is controlled by the main window. Thus the above mentioned crash problem is solved. But if other developer uses the singleton before the window is constructed, the code will crash too. Any good way to solve it? Or we can just accept it because it is developer’s mistake to use it before constructing? Thanks a lot!

Answer 1

You have to use the member initializer list to initialize m_a rather than assign it.
It ensures you don’t have to bother about getting m_a assigned before calling other functions.