6.2.1.5 Pointer to Member Function Types

Pointer to member function objects are stored as a structure with three members, and the layout is equivalent to:

struct { short int d; short int i; union { void (f) (); long 0; } };

The parameter d is the offset to be added to the beginning of the class object for this pointer. The parameter I is the index into the virtual function table, offset by 1. The index enables the NULL pointer to be represented. Its value is -1 if the function is non-virtual. The parameter f is the pointer to the member function if it is non-virtual, when I is 0. The 0 is the offset to the virtual function pointer within the class object.