how to use templated struct within another templated struct (C++)

Question

I am new to C/C++ and trying to template a struct of Point and RectBound to allow for both double and float types.

Here is the Point definition

// simple Point structure                                                           
template <typename T, typename U, typename V>                                       
struct Point{                                                                       
    T x;                                                                            
    U y;                                                                            
    V z; // optional                                                                

    /*                                                                              
    Point(){                                                                        
       x = T();                                                                     
       y = U();                                                                     
       z = V();                                                                     
    }*/                                                                             

    Point(T _x, U _y) {                                                             
        x = _x;                                                                     
        y = _y;                                                                     
    }                                                                               

    Point(T _x, U _y, V _z){                                                        
        x = _x;                                                                     
        y = _y;                                                                     
        z = _z;                                                                     
    }                                                                               

    inline bool equals(Point & p){                                                  
        return(p.x == x && p.y == y);                                               
    }                                                                               

};   

and here is the RectBound structure

// Rectangular Bounds for tree
// T,U should hold double or float only
template <typename T, typename U, typename V>
struct RectBounds {
    // x, y center point   
    T x;
    U y;
    // dimension width w and height h
    T w, h;

    //constructors

    // (_x, _y): center of rectangle bound. (_w, _h): width and height 
    RectBounds(T _x, U _y, T _w, T _h){
        x = _x;
        y = _y;
        w = _w;
        h = _h;
    }

    // returns true if point p is in Rect bounds, false otherwise
    inline bool contains(Point & p) {
        float _w = w/2.0f;
        float _h = h/2.0f;
        return p.x >= x - _w && p.x < x + _w && p.y >= y - _h && p.y < y + _h;
    }

    // returns true if rectangle o intersects this, false otherwise
    inline bool intersects( RectBounds & o){
        float _w = w/2.0f;
        float _h = h/2.0f;
        return !(o.y + o.h/2.0f <= y - _h || o.y - o.h/2.0f >= y + _h || o.x + o.w/2.0f <= x - _w || o.x - o.w/2.0f >= x + _w);
    } 
};

I get the following errors which are expected : (those from the return lines in RectBounds incline function)

error: request for member ‘x’ in ‘p’, which is of non-class type ‘int’
error: request for member ‘x’ in ‘p’, which is of non-class type ‘int’
error: request for member ‘y’ in ‘p’, which is of non-class type ‘int’
error: request for member ‘y’ in ‘p’, which is of non-class type ‘int’

I tried to define a Point within RectBounds class as follows

Point<T,U,V> cp; but that didn't help.

Any suggestions?

Answer 1

First of all, it seems that you've overcomplicating your templates. In a Point , can x , y , and z be different types? I'm guessing not, so you only need one template parameter:

template <typename T>                                       
struct Point{                                                                       
    T x;                                                                            
    T y;                                                                            
    T z;

    // ...
};

The same should be done for RectBounds .

Now, the reason you're actually getting an error is due to the parameter types of your functions contains and intersects . You have used Point and RectBounds . However, these name templates , not types . Function parameters need to have types. Since we have given Point only one template parameter now, a type might be Point<float> . As you can see, we need to provide a template argument. So the following would work:

inline bool contains(Point<float> & p) {

However, it seems that you probably don't want to fix it to some specific type. You either want to accept only Point s that have the same type as the template argument for RectBounds :

inline bool contains(Point<T> & p) {

Or you want to be able to accept Point s with arbitrary type, in which case you can make contains a member function template:

template <typename U>
inline bool contains(Point<U> & p) {