Is a pointer to a virtual member function valid in the constructor of the base class?

Question

My question is not about calling a virtual member function from a base class constructor, but whether the pointer to a virtual member function is valid in the base class constructor.

Given the following

class A
{
    void (A::*m_pMember)();

public:
    A() :
        m_pMember(&A::vmember)
    {
    }

    virtual void vmember()
    {
        printf("In A::vmember()\n");
    }

    void test()
    {
        (this->*m_pMember)();
    }
};

class B : public A
{
public:
    virtual void vmember()
    {
        printf("In B::vmember()\n");
    }
};

int main()
{
    B b;
    b.test();

    return 0;
}

Will this produce "In B::vmember()" for all compliant c++ compilers?

Answer 1

The pointer is valid, however you have to keep in mind that when a virtual function is invoked through a pointer it is always resolved in accordance with the dynamic type of the object used on the left-hand side. This means that when you invoke a virtual function from the constructor, it doesn't matter whether you invoke it directly or whether you invoke it through a pointer. In both cases the call will resolve to the type whose constructor is currently working. That's how virtual functions work, when you invoke them during object construction (or destruction).

Note also that pointers to member functions are generally not attached to specific functions at the point of initalization. If the target function is non-virtual, they one can say that the pointer points to a specific function. However, if the target function is virtual, there's no way to say where the pointer is pointing to. For example, the language specification explicitly states that when you compare (for equality) two pointers that happen to point to virtual functions, the result is unspecified.