C++ Primer, Fifth Edition

15.3. Virtual Functions

As we’ve seen, in C++ dynamic binding happens when a virtual member function is called through a reference or a pointer to a base-class type (§15.1, p. 593). Because we don’t know which version of a function is called until run time, virtual functions must always be defined. Ordinarily, if we do not use a function, we don’t need to supply a definition for that function (§6.1.2, p. 206). However, we must define every virtual function, regardless of whether it is used, because the compiler has no way to determine whether a virtual function is used.

Exercises Section 15.2.3

Exercise 15.8: Define static type and dynamic ...