ambiguous overload : operator(class object, int)

Question

I want to learn template and operator overloading with the purpose : compare length of vector / integer.

ex. (2,5) > 5 ex. (1,0) < (5,2)

This is my template :

    template<class T, class U>
void vectorCmp(T x, U y)
{
    cout<<"Call Function Template"<<endl;

    // operator overloading
    if(x>y)
        cout<<x<<endl;
    else if(y>x)
        cout<<y<<endl;
    else if(x==y)
        cout<<"The length is equal"<<endl;
}

And this is my Vector class :

class Vector
{
    // operator overloading
    friend bool operator>(Vector & v1, Vector & v2);
    friend bool operator>(Vector & v, int l);
    friend bool operator>(int l, Vector & v);
    friend ostream & operator<<(ostream & os, Vector & v);
    friend ostream & operator<<(ostream & os, int l);

    private:
        int x;
        int y;

    public:
        Vector(int x, int y)
        {
            cout<<"Call Vector Constructor"<<endl;
            this->x = x;
            this->y = y;
        }

        ~Vector()
        {
            cout<<"Call Vector Destructor"<<endl;
        }
};

And below is definition of friend function :

    bool operator>(Vector & v1, Vector & v2)
{
    cout<<"Call operator overloading"<<endl;

    if(sqrt(pow(v1.x,2)+pow(v1.y,2))>sqrt(pow(v2.x,2)+pow(v2.y,2)))
        return true;
    else
        return false;
}

bool operator>(Vector & v, int l)
{
    cout<<"Call operator overloading"<<endl;

    if(sqrt(pow(v.x,2)+pow(v.y,2))>l)
        return true;
    else
        return false;
}

bool operator>(int l, Vector & v)
{
    cout<<"Call \'>\'operator overloading"<<endl;

    if(sqrt(pow(v.x,2)+pow(v.y,2))<l)
        return true;
    else
        return false;
}

ostream & operator<<(ostream & os, Vector & v)
{
    os<<"Call \'<<\' operator overloading"<<endl;

    os<<"The biggest length is "<<sqrt(pow(v.x,2)+pow(v.y,2))<<endl;

    return os;
}

ostream & operator<<(ostream & os, int l)
{
    os<<"Call \'<<\' operator overloading"<<endl;

    os<<"The biggest length is "<<l<<endl;

    return os;
}

There are three situations when comparing length of vector/ integer:

-> vector / integer

-> vector / vector

-> integer / vector

and there are two situations to cout:

-> cout << vector

-> cout << integer

Below is my main function :

int main()
{
    int len = 10;
    Vector vec1(12,3);
    Vector vec2(2,5);

    vectorCmp(len,vec1);
    vectorCmp(vec2,len);
    vectorCmp(vec1,vec2);

    return 0;
}

When I compiles, error happens !

error: ambiguous overload for 'operator<<' (operand types are 'std::basic_ostream' and 'int')

I cannot understand why overloading "<<" with integer is error

Thanks for solving my question !

Please provide a minimal reproducible example that will help in answering your question — P.W

Dmitry Gordon Dmitry Gordon · Accepted Answer · 2019-04-23T13:02:40

The reason why you get an error is because you have declared:

ostream & operator<<(ostream & os, int l)

which is ambiguous with the operator of the same signature from the standard library.

ambiguous overload : operator(class object, int)

1 Answers