How do I overload the addition operator to preform commutative calculation?

Question

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Operator Overloading in C++ as int + obj

I have a class A with an overloaded operator+. My problem is that I wish to be able to use summation in the two following ways.

A a;

a + 5;

and

5 + a;

How do I overload + to be able to do this? I am aware that we can overload ++ to perform both post and pre increment (++x and x++), so how can I simulate the above ability as well?

You should look into an operator overloading article or reference for the latter. You can find just about everything [here](http://stackoverflow.com/questions/4421706/operator-overloading). — chris, Nov 02 '12 at 14:31

score 4 · Accepted Answer · answered Nov 02 '12 at 14:30

You define the operator as a non-member:

class A
{
   int operator + (int x) const
   { 
       return 42;
   }
};

inline int operator + (int x, const A& a)
{
   return a+x;  //calls a.operator +(x)
}

The inline is there to prevent defining the symbol multiple times in case you define the operator in a header.

How do I overload the addition operator to preform commutative calculation?

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