C++ Primer Plus

Pointer and Reference Type Compatibility

Dynamic binding in C++ is associated with methods invoked by pointers and references, and this is governed, in part, by the inheritance process. One way public inheritance models the is-a relationship is in how it handles pointers and references to objects. Normally, C++ does not allow you to assign an address of one type to a pointer of another type. Nor does it let a reference to one type refer to another type:

double x = 2.5;int * pi = &x;   // invalid assignment, mismatched pointer typeslong & rl = x;   // invalid assignment, mismatched reference type

However, as you’ve seen, a reference or a pointer to a base class can refer to a derived-class object without using an explicit type cast. For example, ...