Effective C++ Item07

class B {public:B() : str("default constructor") { }B(string in_str) : str(in_str) { }~B() { std::cout << "call B's destructor" << std::endl; }private:string str;};class D : public B{public:D(string in_str) : B(in_str), val(32) {  }~D() { std::cout << "call D's destructor" << std::endl; }int GetVal() { return val; }private:int val;};int _tmain(int argc, _TCHAR* argv[]){D *pD = new D("test Item 7");B *pB;pB = pD;delete pB;std::cout << pD->GetVal() << std::endl;return 0;}