Self assignment check in assignment operator

In C++, assignment operator should be overloaded with self assignment check.

For example, consider the following class Array and overloaded assignment operator function without self assignment check.

// A sample class
class Array {
 private:
   int *ptr;
   int size;
 public:
   Array& operator = (const Array &rhs);
   // constructors and other functions of class........
};

// Overloaded assignment operator for class Array (without self
// assignment check)
Array& Array::operator = (const Array &rhs)
{
  // Deallocate old memory
  delete [] ptr;

  // allocate new space
  ptr = new int [rhs.size];

  // copy values
  size = rhs.size;
  for(int i = 0; i < size; i++)
    ptr[i] = rhs.ptr[i];

  return *this;
}

If we have an object say a1 of type Array and if we have a line like a1 = a1 somewhere, the program results in unpredictable behavior because there is no self assignment check in the above code. To avoid the above issue, self assignment check must be there while overloading assignment operator. For example, following code does self assignment check.

// Overloaded assignment operator for class Array (with self
// assignment check)
Array& Array::operator = (const Array &rhs)
{
  /* SELF ASSIGNMENT CHECK */
  if(this != &rhs)
  {
    // Deallocate old memory
    delete [] ptr;

    // allocate new space
    ptr = new int [rhs.size];

    // copy values
    size = rhs.size;
    for(int i = 0; i < size; i++)
      ptr[i] = rhs.ptr[i];
  }

  return *this;
}

References:
http://www.cs.caltech.edu/courses/cs11/material/cpp/donnie/cpp-ops.html

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