What are the rules for calling the superclass constructor?

c++ inheritance constructor
levik picture levik · Sep 23, 2008 · Viewed 826.5k times · Source

What are the C++ rules for calling the superclass constructor from a subclass one?

For example, I know in Java, you must do it as the first line of the subclass constructor (and if you don't, an implicit call to a no-arg super constructor is assumed - giving you a compile error if that's missing).

Answer

luke picture luke · Sep 23, 2008

Base class constructors are automatically called for you if they have no argument. If you want to call a superclass constructor with an argument, you must use the subclass's constructor initialization list. Unlike Java, C++ supports multiple inheritance (for better or worse), so the base class must be referred to by name, rather than "super()".

class SuperClass
{
    public:

        SuperClass(int foo)
        {
            // do something with foo
        }
};

class SubClass : public SuperClass
{
    public:

        SubClass(int foo, int bar)
        : SuperClass(foo)    // Call the superclass constructor in the subclass' initialization list.
        {
            // do something with bar
        }
};

More info on the constructor's initialization list here and here.

Related questions

Inheriting constructors

Why does this code: class A { public: explicit A(int x) {} }; class B: public A { }; int main(void) { B *b = new B(5); delete b; } Result in these errors: main.cpp: In function ‘int main()’: main.cpp:13: error: no matching function …

Read More
Calling the base class constructor from the derived class constructor

I have a question: Say I have originally these classes which I can't change (let's say because they're taken from a library which I'm using): class Animal_ { public: Animal_(); int getIdA() { return idA; }; string getNameA() { return nameA; } private: string nameA; …

Read More
Using C++ base class constructors?

While working with templates I ran into a need to make a base class constructors accessible from inherited classes for object creation to decrease copy/paste operations. I was thinking to do this through using keyword in same manner with …

Read More