Question

I want to create my own Point struct it is only for purposes of learning C++.
I have the following code:

template <int dims, typename T>
struct Point {
    T X[dims];
    Point(){}
    Point( T X0, T X1 ) {
        X[0] = X0;
        X[1] = X1;
    }
    Point( T X0, T X1, T X2 ) {
        X[0] = X0;
        X[1] = X1;
        X[2] = X2;
    }
    Point<dims, int> toint() {
        //how to distinguish between 2D and 3D ???
        Point<dims, int> ret = Point<dims, int>( (int)X[0], (int)X[1]);
        return ret;
    }
    std::string str(){
        //how to distinguish between 2D and 3D ???
        std::stringstream s;
        s << "{ X0: " << X[0] << " | X1: " <<  X[1] << " }";
        return s.str();
    }
};
int main(void) {

    Point<2, double> p2d = Point<2, double>( 12.3, 45.6 );
    Point<3, double> p3d = Point<3, double>( 12.3, 45.6, 78.9 );

    Point<2, int> p2i = p2d.toint(); //OK
    Point<3, int> p3i = p3d.toint(); //m???

    std::cout << p2d.str() << std::endl; //OK
    std::cout << p3d.str() << std::endl; //m???
    std::cout << p2i.str() << std::endl; //m???
    std::cout << p3i.str() << std::endl; //m???

    char c; std::cin >> c;
    return 0;
}

of couse until now the output is not what I want.
my questions is:
how to take care of the dimensions of the Point (2D or 3D) in member functions of the Point?

many thanks in advance
Oops

Answer 1

Your dimensions are fixed at compile time, by the template arguemnt dims, so you can iterate over them:

std::string str(){
    //how to distinguish between 2D and 3D ???
    std::stringstream s;
    s << "{ ";
    std::copy( X, X+dims, std::ostream_iterator<T>( s, "|") );
    s << " }";
    return s.str();    
}

Also, you can provide a constructor in terms of the dims:

Point( const T (&c) [dims] ){
  std::copy( c, c+dims, X );
}

This allows for code like double[] d={1,2,3}; Point<3,double> p(d);, which puts the decision on the number of arguments elsewhere.

For the ‘cast-to-point-of-ints’ constructor you just can use Point as the argument:

Point<dims,int> toint() const {
    Point<dims,int> result;
    std::copy( X, X+dims, result.X );
    return result;
}