CODEWITHSUNDEEP
c++operator-overloading
masan
masan

Reputation: 23

c++ Operator overload - What operand type am i actually returning?

I'm trying to overload some operators for my Vector class, but is getting below error when trying to to assert(v+v == v*2):

[Error] no match for 'operator==' (operand types are 'Vector' and 'Vector').

When using assert(v==v) the function works fine, and I'm also able to create new vectors using the + and * operator. 

class Vector{

private:    
    vector<double> arr;  

    friend bool operator ==(  Vector &src,  Vector &src2) {
        int z = src.size();     
        if (z != src2.size()){
            return false;
        }

        for (int i = 0;  i < src.size(); i++){
            double p = src.at(i);
            if (p != src2.at(i)){ 
                return false;
            }
        };
        return true;
        };

    friend Vector operator +(Vector &src, Vector &src2)  {
        Vector TEMP = src;      
        for (int i = 0;  i < src.size(); i++){
            TEMP.arr[i] = src.arr[i] + src2.arr[i];
        }
        return TEMP;
    };

    friend Vector operator *(Vector &src, const int x) {
        Vector TEMP = src;
        for (int i = 0;  i < src.size(); i++){
            TEMP.arr[i] = src.arr[i] *x;
        }
        return TEMP;
        };

};


int main() {

  double data1[] = {3.4, 4.4, 6.0};
  Vector v(sizeof(data1)/sizeof(double), data1);
  assert(v == v);
  assert(v + v == v * 2);


};

Upvotes: 2

Views: 69

Answers (1)

songyuanyao
songyuanyao

Reputation: 173024

You declare the parameter type of operator == as lvalue reference to non-const. But both operator + and operator * return by value, what they return are rvalues; which can't be bound to lvalue reference to non-const.

You can change the parameter type of operator== to lvalue reference to const, which could bind to rvalues. (And they don't need to be lvalue reference to non-const, because operator== is not supposed to perform modification.) e.g.

friend bool operator ==(const Vector &src, const Vector &src2) {
    ...
}

Upvotes: 3

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