question about polymorphism in c++

[tpopono]

Hello, im starting out in c++ and i want to know why this code prints out base

struct base 
{
    virtual void foo(void){
        cout<<"base"<<endl;
    }
 }
 struct derived : base(void)
 {
   void foo(void){
       cout<<"derived"<<endl;
   }
 }
 
int main (void)
 {
 base *b = new derived;
 b -> foo();
 return 0
 }

i know that when making a program like this in java the output would be derived.. I would like to know how it works in c++. thank you for your time