The compiler keeps saying 'class A' has no member named 'foo'. I am trying to use a function from a derived class with a pointer. Here is my code:
class A{ ..... }; class B:public A{ virtual void foo() = 0; }; class C:public B{ .... public: void foo(){ .... } }; I have a table of A pointers named Table and when trying
Table[j]->foo() I am getting the compiler error.
What should I do except cast?
You have a compilation error because function foo is not declared in class A.
You can declare it as pure virtual in A like this:
class A { virtual void foo() = 0; }; In derived classes you don't have to declare foo as explicitly virtual. If only C is a concrete class, you don't have to declare foo in class B at all.
If your example if you know that in your array of pointers to A you have only instances of class C you can explicitly cast to pointer to C but it is a sign of poor design and I don't recommend it:
static_cast<C*>(Table[j])->foo() If you have a pointer to a base and want to access a member of the derived type you have to cast so you have a pointer to the derived type, either that or as in your case add foo() as a virtual member to the base.
class A { ... }; class B : public A:{ { public: virtual foo() { std::cout << "B::foo" << std::endl; } }; class C : public B { public: void foo() { std::cout << "C::foo" << std::endl; }; ... A * arr[8]; for(int i = 0; 8>i; ++i) arr[i] = new C; ((B*)arr[0])->foo(); // will print "C::foo\n" But if you added virtual void foo() = 0; to A then you could just do arr[0]->foo() and it would still print C::foo
static_cast or dynamic_cast here.
A? That's the type you actually try to use polymorphically.B. It won't have it.