Using == Operator with Classes

[mikeman118]

Hi,

Like the tile says, would it be possible to use the == operator with a class? For example:

class Class
{
    ...
}
Class cls1, cls2;
if (cls1 == cls2)
{
    ...
}

If it's difficult or something complicated then never mind, but if it's not too difficult can anyone tell me how to do this? Thanks.

[Salem]

http://www.parashift.com/c++-faq-lit...erloading.html
Any decent reference material should tell you how to do this.

[CornedBee]

Yes. You just have to overload it. Either as a free function:

bool operator ==(const Class &lhs, const Class &rhs)
{
  return codeThatDeterminesIfLhsAndRhsAreEqual();
}

Or as a member function.

bool Class::operator ==(const Class &rhs)
{
  return codeThatDeterminesIfThisAndRhsAreEqual();
}

[matsp]

You need to declare an "operator==(const Class &rhs)" in your class - or you can declare an external "operator==(const Class &lhs, const Class &rhs)". [1]

You then need to "compare" your two elements (*this, rhs or lhs, rhs depending on which you choose). For example:

class C 
{
private:
   int x;
   int y;
...
public:
   bool operator==(const C &rhs)
   {
      if (rhs.x == x && rhs.y == y) return true;
      return false;
   };
};

Of course, depending on the contents of your class, the comparison may be more or less complex, and you don't necessarily need to compare ALL the fields. If a record is a "person", then "social security number" or similar may be the component that says two persons are the same [obviously, that would have to be checked elsewhere that two different persons aren't entered with the same number]. Or a car-registration number for a car, serial number for a computer, etc.


[1] lhs stands for Left Hand Side and rhs stands for Right Hand Side, and corresponds to the left and right hand side operands to the == operator.

--
Mats

[mikeman118]

Thank you everyone, it worked! (That was easy)