Protected data in parent class not available in child class?

Question

I am confused: I thought protected data was read/writable by the children of a given class in C++.

The below snippet fails to compile in MS Compiler

Answer 1

You just shouldn't copy an A object in a B constructor. The intention is to leave the initialization of A's members to it's own constructor:

struct A { 
  A( const A& a ): data( a.data ) {}
  protected: int data; 
};

struct B : public A {
  B( const A& a ): A( a ) {}
};