Is derived class?

[packetVB]

Ok,
Given classes
Base class vBase
and Derived class vLabel and vTextBox

is there a way to determine in the base class which derived class a base class pointer is pointing too?


packetvb

[parksie]

Use typeid:

#include <iostream>
#include <typeinfo>

using namespace std;

class base {
public:
    // must be polymorphic base class for typeid to work
    virtual void something() { };
    int a;
};
class derived_a : public base { char b; };
class derived_b : public base { double c; };

int main() {
    base *a = new derived_a;
    base *b = new derived_b;
    base *c = new base;
    
    cout << "typeid(a): " << typeid(a).name() << endl;
    cout << "typeid(b): " << typeid(b).name() << endl;
    cout << "typeid(c): " << typeid(c).name() << endl;
    cout << "typeid(*a): " << typeid(*a).name() << endl;
    cout << "typeid(*b): " << typeid(*b).name() << endl;
    cout << "typeid(*c): " << typeid(*c).name() << endl;

    delete a; delete b; delete c;
}

For typeid to give the correct type information, the base class must be a polymorphic class; that is, it has at least one virtual member (in your situation, virtual methods are probably already needed).

Note that using typeid on the pointer produces the obvious result that it's a pointer to base. Dereferencing the pointer (here's where the virtual method is needed) looks up the actual type, and sees where it is.

Note that the typeinfo::name() output is *not* portable across compilers...if you wish to verify types, you can use something like:

if(typeid(*a) == typeid(derived_a)) { /* lar */ };

[CornedBee]

Note that you must explicitely enable RTTI for some compilers.