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Overloading =

Posted on 1998-02-06
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Last Modified: 2010-04-10
I tried overloading the operator=, but it doesn't get called inside my Function(). It does not displays the
message box in the overloaded operator=. What is wrong?

// in header file
MyObject& operator= (const MyObject&);

// in cpp file
MyObject& MyObject::operator= (const MyObject& that)
{
  AfxMessageBox("Here") ;
  x = that.x;  
  return *this;
}

void MyObjec::Function()
{
  MyObject *pObj = new MyObject(1) ;
  MyObject *pTemp = pObj ;
}

leow
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Question by:engllf
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3 Comments
 
LVL 15

Accepted Solution

by:
Tommy Hui earned 40 total points
ID: 1181048
That is because you are assigning pointers and not references. To use the assignment operator, you need references:

  MyObject temp;
  temp = *pObj;

Note that you need to do it in two steps and not

  MyObject temp = *pObj;

which will call the copy constructor instead:

  MyObject(const MyObject& rhs);


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Author Comment

by:engllf
ID: 1181049
Hi thui,

Then do i need to overload the operator= if i am assigning pointers?

engllf

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LVL 15

Expert Comment

by:Tommy Hui
ID: 1181050
You can only overload operator= for classes you define. You cannot override assignment operators for pointer to classes. For example this is possible to override because the left hand side is an object:

  MyObject temp;
  MyObject o1;
  MyObject* p2;
  temp = o1;   // MyObject::operator = (MyObject rhs);
  temp = p2;   // MyObject::operator = (MyObject* rhs);

However, these are NOT possible because the left hand side of the = is a pointer:

  MyObject* pTemp2;
  MyObject o1;
  MyObject* p2;

  pTemp2 = o1;  // Not possible
  pTemp2 = p2;  // Not possible

But this is because *pTemp2 is an object:

  *pTemp2 = o1;
  *pTemp2 = p2;

  MyObject* pTemp;
   
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