How to overload...

Sep 5, 2012 at 8:52am
Aceix (1118)
How do I overload the == operator.

MANN, I have big problems in overloading operators!!!
Who can give me a different tut that talks of overloading operators and the keyword this.
Last edited on Sep 5, 2012 at 8:54am
Sep 5, 2012 at 9:11am
kbw (9488)
There are two ways you can implement operator == for your class. You can define it as a class method or as non-member function.

This demonstrates the class method.
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class Complex
{
    int real, imaginary;

public:
    int getReal() const { return real; }
    int getImaginary() const { return imaginary; }

    bool operator==(const Complex &param) const
    {
        return param.getReal() == getReal() && param.getImaginary() == getImaginary();
    }
    //...
};


This demonstrates the non-member function:
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class Complex
{
    int real, imaginary;

public:
    int getReal() const { return real; }
    int getImaginary() const { return imaginary; }
    //...
};

bool operator==(const Complex &lhs, const Complex &rhs)
{
        return lhs.getReal() == rhs.getReal() && lhs.getImaginary() == rhs.getImaginary();
}
Last edited on Sep 5, 2012 at 9:14am
Sep 5, 2012 at 9:11am
closed account (o3hC5Di1)
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bool operator==(myclass& a, myclass& b)
{
    return (a.value == b.value);
}

// or within myclass:

bool myclass::operator==(myclass& b)
{
    return (value == b.value);  //the current object is used as the left operand
}


If you let us know what part you're having trouble with understanding someone might be able to give you a more in depth explanation.

All the best,
NwN

Sep 5, 2012 at 9:13am
closed account (zb0S216C)
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// Through a class:
struct Sample
{
    bool operator == (Sample const &right) const;
};

// Globally:
bool operator == (Sample const &left, Sample const &right);

Wazzak
Sep 5, 2012 at 9:15am
Aceix (1118)
Thanks... any tutorial?
Sep 5, 2012 at 9:20am
MrHutch (1822)
If I overloaded the == operator, I'd probably expect it to return a boolean.

The keyword this is just a self reference to the class your working with.

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// Example
// I'll make the class public for ease of testing

class Foo
{
public:
   int m_int;
   char m_char;
   Foo(int i, char c):m_int(i), m_char(c){}
   bool operator ==(const Foo &other) const
   {
      if (this->m_int  == other.m_int &&
          this->m_char == other.m_char)
     {
         return true;
     }
     return false;
   }
};

// In main
Foo a(10, 'a');
Foo b(10, 'a');

if (a == b)
{
   cout << "Same" << endl;
}
else
{
   cout << "Not same" << endl;
}


Does this example help at all? This overloaded operator returns true if both the m_int and m_char variables are the same for the two classes. If either or both differ, it'll return false.


Edit: Holy crap. I got ninja'd multiple times while writing that one. ¬_¬
Last edited on Sep 5, 2012 at 9:21am
Sep 5, 2012 at 9:55am
Zephilinox (595)
just look at an example, any example, you don't need a tutorial, its just a function in a class with a very specific name and two arguments, the body of which compares variables of one class with the other, if they are all equal return true, otherwise return false.
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