C++自动析构时的顺序问题

//普通(非模板)类的成员模板
class DebugDelete{
public:
 DebugDelete(ostream &s = cerr) :os(s){}
 template <typename T>void operator()(T*p)const
 {
 os << "deleting unique_ptr " <<typeid(T).name() <<endl;
 delete p;
 }
private:
 ostream &os;
};
void demo_general_class_tempalte_member()
{
 double *p = new double;
 DebugDelete d;
 d(p);//d调用DebugDelet::operator()(double*),释放p
 int* ip = new int;
 //在一个临时DebugDelete 对象上调用operator()(int*)
 DebugDelete()(ip);
 //实例化DebugDelete::opeartor()<int>(int*)const
 unique_ptr<int, DebugDelete>p2(new int, DebugDelete());
 //实例化DebugDelete::opeartor()<string>(string*)const
 unique_ptr<string, DebugDelete>sp(new string, DebugDelete());
}

class B
{
public:
 virtual ~B(){ cout << "delete B" << endl; }
};
class D :B
{
public:
 virtual ~D() override{ cout << "delete D" << endl; }
};
void demo_delete()
{
 D d;
}

class A
{
public:
 int _Id; 
 A():_Id(0)
 {
 printf("A[%d]\n",_Id);
 }

~A()
 {
 printf("~A[%d]\n",_Id);
 }
};

class B
{
public:
 A _A;
 A* _PA;
 B()
 {
 printf("B\n");
 }
 ~B()
 {
 printf("~B\n");
 delete _PA;
 }
};

int main(int argc, char* argv[])
{
 {
 B b;
 b._PA = new A();
 b._PA->_Id = 17;
 }

 return 0;
}