cpp pointer

test1.cpp

#include <iostream>

using namespace std;

int main(){
    int a = 3;
  
    int *p, *q;
    p = &a;
    q = p;
    cout << p << ", " << q << endl;
    cout << *p << ", " << *q << endl;
    delete p;
    //cout << p << ", " << q << endl;
    //if (p == NULL){
    //    cout << "p is null" << endl;
    //}

    if (q == NULL){
        cout << "q is null" << endl;
    }
    //cout << *q << endl;
    return 0;
}

test2.cpp

// operator delete example
#include <iostream>     // std::cout

using namespace std;

struct MyClass {
  MyClass() {std::cout <<"MyClass constructed\n";}
  ~MyClass() {std::cout <<"MyClass destroyed\n";}
  void t(){
     cout << "hello" << endl;
  }
};

int main () {
  MyClass * pt = new (std::nothrow) MyClass;
  cout << "1" << endl;
  MyClass * q = new (std::nothrow) MyClass;
  cout << "2" << endl;
  q = pt;
  cout << "3" << endl;
  delete pt;    // implicitly calls ::operator delete(pt)
  cout << "4" << endl;
  q->t();
  return 0;
}