C++ Derived to base conversion for pointers to members


Example

A pointer to member of derived class can be converted to a pointer to member of base class using static_cast. The types pointed to must match.

If the operand is a null pointer to member value, the result is also a null pointer to member value.

Otherwise, the conversion is only valid if the member pointed to by the operand actually exists in the destination class, or if the destination class is a base or derived class of the class containing the member pointed to by the operand. static_cast does not check for validity. If the conversion is not valid, the behaviour is undefined.

struct A {};
struct B { int x; };
struct C : A, B { int y; double z; };
int B::*p1 = &B::x;
int C::*p2 = p1;                              // ok; implicit conversion
int B::*p3 = p2;                              // error
int B::*p4 = static_cast<int B::*>(p2);       // ok; p4 is equal to p1
int A::*p5 = static_cast<int A::*>(p2);       // undefined; p2 points to x, which is a member
                                              // of the unrelated class B
double C::*p6 = &C::z;
double A::*p7 = static_cast<double A::*>(p6); // ok, even though A doesn't contain z
int A::*p8 = static_cast<int A::*>(p6);       // error: types don't match