I have class A and B.
class A{ public: foo(); }; class B : public A{ public: int x; }; Assume that there is an object from B class in a test file.How should I call foo function?
object.foo(); // or object.A::foo(); Other questions: When do we call a function like that?What if I do multiple inheritance?
Simply object.foo(), and there's not much more to add:
B object; object.foo(); class B inherits public members of class A, so function foo() also belongs to class B and can be called using B class's object.
B b; b.foo(); You need to know inheritance in c++. Its just same as
b.x; See x and foo() both are member of object b even b is object of Class B and its possible because Class B inheritance features from Class A, In your code function foo().
Note Class A has only one member function foo()
A a; a.foo(); Is valid, But
a.x; Is not valid
EDIT: Multi-level inheritance Class C inherits Class B and Class B inherits Class A, then
class C : public B{ public: int y; }; C c; c.foo(); // correct Is also valid.
And
c.x; c.y; Also valid, x, y, foo() all are member of Class C.
Notice: What I told you is multi-level Multiple inheritance in C++ is different. Also three access specifiers in C++ are very important in case of inheritance: public private protected in c++
private, public and protected inheritance in C++