C++ Primer, Fifth Edition

Calls to Virtual Functions May Be Resolved at Run Time

When a virtual function is called through a reference or pointer, the compiler generates code to decide at run time which function to call. The function that is called is the one that corresponds to the dynamic type of the object bound to that pointer or reference.

As an example, consider our print_total function from §15.1 (p. 593). That function calls net_price on its parameter named item, which has type Quote&. Because item is a reference, and because net_price is virtual, the version of net_price that is called depends at run time on the actual (dynamic) type of the argument bound to item:

Quote base("0-201-82470-1", 50);print_total(cout, base, 10);    // calls Quote::net_priceBulk_quote ...