What's the right behavior when auto meets polymorphism and virtual function?

Question

class B {
    public:
    virtual void f(){
        printf("B\n");
    }
};
class D : public B { 
    public:
    void f() {
        printf("D\n");
    }
};

int main(void)  
{  
    B* d = new D();
    d->f();
    auto b = *d; 
    b.f();
}

for d->f();, the output is D. this is right. But for b.f();, the output is B. Is this right?

Answer 1

Is this right?

It's right, the type is deduced at compile time. auto uses the same rules of template argument deduction for type deduction, based on the static type, dynamic polymorphism won't be considered.

For this case, the type of d is B*, then type of *d is B, so the type of b is just B. Then *d will be slicing copied to b, for b.f() B::f() should be invoked.

The code is equivalent to the following which might be clearer.

B b = *d;
b.f();