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As you’ve seen, the constructor for a base class is automatically called when an object of a derived class is instantiated, but you can also explicitly call a base class constructor from a derived class constructor. The syntax for this is a lot like the syntax for a member initialization list. To call a base class constructor from a derived class constructor, after the derived constructor’s parameter list, type a colon followed by the name of the base class, followed by a set of parentheses containing whatever parameters the base class constructor you’re calling needs. I do this in the Boss constructor, which says to explicitly call the Enemy constructor and pass it damage.
Boss::Boss(int damage):
Enemy(damage) //call base class constructor with argument
{}
This allows me to pass the Enemy constructor the value that gets assigned to
m_Damage, rather than just accepting its default value.
When I first instantiate aBoss in main(), the Enemy constructor is called and passed the value 30, which gets assigned to m_Damage. Then, the Boss constructor runs (which doesn’t do much of anything) and the object is completed.
344 Chapter 10 n Inheritance and Polymorphism: Blackjack
Hi n t
Being able to call a base class constructor is useful when you want to pass specific values to it.
