C++ Primer, Fifth Edition

19.2.1. The dynamic_cast Operator

A dynamic_cast has the following form:

dynamic_cast<type*>(e)dynamic_cast<type&>(e)dynamic_cast<type&&>(e)

where type must be a class type and (ordinarily) names a class that has virtual functions. In the first case, e must be a valid pointer (§ 2.3.2, p. 52); in the second, e must be an lvalue; and in the third, e must not be an lvalue.

In all cases, the type of e must be either a class type that is publicly derived from the target type, a public base class of the target type, or the same as the target type. If e has one of these types, then the cast will succeed. Otherwise, the cast fails. If a dynamic_cast to a pointer type fails, the result is 0. If a dynamic_cast to a reference type fails, the operator ...