c++ inheritance question

Question

I have a question about this:

class A
{
  int a;
  int* pa;
public:
   A(int i):a(i) , pa(new int(a))
   {
      cout<<"A ctor"<<a<<endl;
   }
   ~A()
    {
      delete pa;
      cout<<"dtor\n";
    }
    int * &get()
    {
     return pa;
    }
};

class B : public A
{
     int b;
public:
      B (A obj): A(obj) , b(0)
      {
       cout<<"B ctor\n";
      }
      ~B()
      {
       cout<<"B dtor\n";
      }
};

int main()
{
 int i = 23 ; 
 A* p = new B(i);
}

Can tell me why the last line in main compiles? I pass an int into B's constructor which expects an A object instead. I believe that the int is translated to an A in B's constructor, but why?

Thanks in advance.

Avri.

Answer 1

Since you have not declared A constructor as explicit compiler is creating an anomymous instance of A using i and using it to initialize B instance. If you don't want the compiler to do these implicit conversions declare your costructor as explicit. Then you will get a compiler error.