Question

Possible Duplicate:
Calling virtual functions inside constructors

main.cpp

#include <iostream>

class BaseClass {

    public:

    BaseClass() {
        init();
    }

    virtual ~BaseClass() {
        deinit();
    }

    virtual void init() {
        std::cout << "BaseClass::init()\n";
    }

    virtual void deinit() {
        std::cout << "BaseClass::deinit()\n";
    }

};

class SubClass : public BaseClass {

    public:

    virtual void init() {
        std::cout << "SubClass::init()\n";
    }

    virtual void deinit() {
        std::cout << "SubClass::deinit()\n";
    }

};

int main() {
    SubClass* cls = new SubClass;
    delete cls;
    return 0;
}

Why is init() and deinit() not properly overriden and the BaseClasses’ methods are called instead of the SubClasses ones? What are the requirements to make it work?

BaseClass::init()
BaseClass::deinit()

Answer 1

Because you are calling a virtual method inside a constructor. While constructing Base class the derived one (SubClass) isn’t still constructed, so actually it doesn’t still exist.

It’s generally a good practice to avoid calling virtual methods inside constructors.