VC warning C4251

In a VC dll project, when we export a class which contains a not exported class variable, VC will have a warning(C4251).

For example,

class A
{
private:
    int m_i;
};

class __declspec(dllexport) B
{
private:
    A m_a;
};

VC will complain:

warning C4251: 'B::m_a' : class 'A' needs to have dll-interface to be used by clients of class 'B'

To work around this problem, we can change the member variable definition like below:

class A
{
private:
    int m_i;
};


class __declspec(dllexport) B
{
private:
    A* m_pa;
};