question regarding "this" pointer in c++

Question

i have been given class with int variables x and y in private, and an operator overload function,

class Bag{
private:
    int x;
    int y;
public:
    Bag();
    ~Bag();
    //.......
    //.....etc
};


Bag operator+ (Bag new) const{
    Bag result(*this);   //what does this mean?
    result.x += new.x;         
    result.y += new.y;
}

What is the effect of having "Bag result(*this);" there?.

Answer 1

Bag result(*this) creates a copy of the object on which the operator function was called.

Example if there was:

sum = op1 + op2; 

then result will be a copy of op1.

Since the operator+ function is doing a sum of its operands and returning the sum, we need a way to access the operand op1 which is done through the this pointer.

Alternatively we could have done:

Bag result;
result.x = (*this).x + newobj.x; // note you are using new which is a keyword.
result.y = (*this).y + newobj.y; // can also do this->y instead
return result;