que on Pointer to a class instance which is stored in a global variable

[hanna88]

here's the overview what ive done so far:

 
class A{};
class B{};public A
class C{}:public A
 
//i need to create a function that keep track 
//of num of active B and C instance
//in other file.cpp and file.h 
 
std::vector<A*> getsize();
 
 
 

im not sure whether im on the right track by
solving this using pointers to a class instance which store in global function?
in this case what does type A* means?

any help would be great.

cheers

[Banfa]

A * is exactly what it looks like. A pointer to type A. However if A is polymorphic through the use of virtual functions then you can use an A * to point to an instance of B or C and when you call the virtual functions via the A * base pointer it will actually call the implementations of the functions in B or C.

If your functions in A are not polymorphic (declared virtual) then when you call them on an instance of B or C through a base class pointer A * it will call the function defined in A.

This may make more sence with an example

class A
{
public:
    A();
    virtual ~A(); /* Very important on a polymorphic/abstract 
                      class to declare destructor virtual */
 
    void nonVirtualFun();
    virtual void virtualFun();
}
 
class B : A
{
public:
    B();
    virtual ~B(); /* Very important on a polymorphic/abstract 
                      class to declare destructor virtual */
 
    void nonVirtualFun();
    virtual void virtualFun();
}
 
B *myB = new B;    // Create a B
A *basePtr = myB;    // Take a base class pointer to it
 
myB->nonVirtualFun(); // Calls B::nonVirtualFun
A->nonVirtualFun(); // Calls A::nonVirtualFun
 
myB->virtualFun(); // Calls B::virtualFun
A->virtualFun(); // Calls B::virtualFun
 
delete myB;