Question

I’m a bit confused with classes was hoping some one could explain.

I have a class I’m making to create buttons for a game menu. There are four variables:

int m_x
int m_y
int m_width
int m_height

I then want to use a render function in the class but Im not understanding how i use the 4 int variables in the class and pass it to the function in the class?

My class is like this:

class Button
{
private:
    int m_x, m_y;            // coordinates of upper left corner of control
    int m_width, m_height;   // size of control

public:
Button(int x, int y, int width, int height)
{
   m_x = x;
   m_y = y;
   m_width = width;
   m_height = height;
}

void Render(SDL_Surface *source,SDL_Surface *destination,int x, int y)
{
    SDL_Rect offset;
    offset.x = x;
    offset.y = y;

    SDL_BlitSurface( source, NULL, destination, &offset );
}


} //end class

Where i am confused is how the values created in public:Button is passed to void render I’m not fully sure I’ve got this right, if i have its pure luck so far because I’m still a little bit confused.

Answer 1

Maybe an example will help:

#include <iostream>
class Button
{
private:
    int m_x, m_y;            // coordinates of upper left corner of control
    int m_width, m_height;   // size of control

public:
    Button(int x, int y, int width, int height) :
        //This is initialization list syntax. The other way works,
        //but is almost always inferior.
        m_x(x), m_y(y), m_width(width), m_height(height)
    {
    }

    void MemberFunction()
    {
        std::cout << m_x << '\n';
        std::cout << m_y << '\n';
        //etc... use all the members.
    }
};


int main() {
    //Construct a Button called `button`,
    //passing 10,30,100,500 to the constructor
    Button button(10,30,100,500);
    //Call MemberFunction() on `button`.
    //MemberFunction() implicitly has access
    //to the m_x, m_y, m_width and m_height
    //members of `button`. 
    button.MemberFunction();
}