Question

#include <iostream>

using namespace std;

class Object{};

class Connection
{
  public:
    Connection(Object * _obj);
    Object * obj;
    void status();
};

Connection::Connection(Object * _obj)
{
  obj = _obj;
}

void Connection::status()
{
  cout << obj << endl;
}


int main() {
  Object * myObj = new Object();

  Connection * myConn = new Connection(myObj);

  delete myObj;
  myObj = NULL;

  cout << myObj << endl;
  myConn->status();
  /*
  Output is:

  0
  0x25ec010

  but should be:

  0
  0

  */
}

I thought I am only working with pointers in this example. So I don’t understand why the pointer in “myConn” is not set to NULL too, because there are two pointers which point to the same address.

Answer 1

It shouldn’t be 0 because you are copying pointer value. Try using references (&) instead.

Maybe this is not a best example, and boost::shared_ptr will be better solution, but this code will work:

 // skipped...
 class Connection
 {
 public:
   Connection(Object **_obj);
   Object **obj;
   void status();
 };

 Connection::Connection(Object **_obj) : obj(_obj) { }
 void Connection::status() { cout << *obj << endl; }

 int main()
 {
   Object * myObj = new Object();
   Connection * myConn = new Connection(&myObj);
 // skipped