C++ Primer, Fifth Edition

Virtual Functions and Default Arguments

Like any other function, a virtual function can have default arguments (§ 6.5.1, p. 236). If a call uses a default argument, the value that is used is the one defined by the static type through which the function is called.

That is, when a call is made through a reference or pointer to base, the default argument(s) will be those defined in the base class. The base-class arguments will be used even when the derived version of the function is run. In this case, the derived function will be passed the default arguments defined for the base-class version of the function. If the derived function relies on being passed different arguments, the program will not execute as expected.

Best Practices

Virtual functions ...