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c++polymorphismshared-ptr

Is it possibile to call virtual methods with shared pointers?

class Base {
public:
    virtual void f() const { std::cout << "Base::f()" << std::endl; }
};

class Derived : public Base {
public:
    void f() const { std::cout << "Derived::f()" << std::endl; }
};

int main()
{
    Base* obj = new Derived;
    std::shared_ptr<Base> sp = std::make_shared<Base>(*obj);
    sp->f();  //prints Base::f()
}

What i expect is that sp->f() prints Derived::f(), just like raw pointers with virtual methods. What is the correct way to have a polymorphic behaviour with std::shared_ptr?

Solution

  • sp points to an instance of type Base, not Derived. You can't clone derived classes using a pointer to base like this.

    std::shared_ptr<Base> sp = std::make_shared<Derived>(); would work. ... =std::make_shared<Derived>(std::dynamic_cast<Derived&>(*obj)) would also work;