CODEWITHSUNDEEP
c++abstract-classsfml
Petahwil
Petahwil

Reputation: 447

Abstract Class Error In C++ SFML

Hello all I though it would be fun exercise to try to make a Sierpinski Triangle and I am having an issue with this abstract class error that I can't seem to figure out. When I try to make a SierpinskiTri "SierpinskiTri sierpinskiii;" object and then draw it to the window "window.draw(sierpinskiii);" i get an error on that object saying it is an abstract class 

class SierpinskiTri : public sf::Drawable{
public :

SierpinskiTri(sf::RenderWindow &window):m_window(window) {
    //filledTriangle(300, 400, 300);
    sierpinski(3 ,300, 0,300);
     }

virtual void sierpinski(int n, double x, double y, double s){

        filledTriangle(x, y, s);
        sierpinski(n-1, x - s/2, y, s/2);
        sierpinski(n-1, x + s/2, y, s/2);
        sierpinski(n-1, x, y+sqrt(3)/2*s, s/2);

    if(n == 0)
    {
        return;
    }
}


virtual void filledTriangle(float x, float y, float s){
    float* xl = new float[4];
    xl[0] = x - s/2; xl[1]= x + s/2;  xl[2]  = x; xl[3] = x-s/2;
    float* yl = new float[4];
    yl[0] = sqrt(3)/2*s+y; yl[1] = yl[0]; yl[2] = y; yl[3] = yl[0];

    draw(xl,yl,m_window);

}
private:
sf::RenderWindow &m_window;

virtual void draw(float xl[],float yl[],sf::RenderWindow &window) const {

sf::VertexArray triangle(sf::Triangles, 3);

 triangle[0].position = sf::Vector2f(xl[0],yl[1]);
 triangle[0].color = sf::Color::Blue;  
 triangle[1].position = sf::Vector2f(xl[1],yl[1]);
 triangle[1].color = sf::Color::Red;
 triangle[2].position = sf::Vector2f(xl[2],xl[2]);
 triangle[2].color = sf::Color::White;
 window.draw(triangle);
}


};

Upvotes: 1

Views: 486

Answers (2)

Öö Tiib
Öö Tiib

Reputation: 11011

By documentation you have to override that function:

virtual void sf::Drawable::draw( RenderTarget& target
                               , RenderStates states ) const;

You have written that function:

virtual void draw( float xl[]
                 , float yl[]
                 , sf::RenderWindow &window ) const;

As result your derived class is abstract like compiler tells. In order to override you need to match the signature of virtual function correctly.

Upvotes: 2

Barry
Barry

Reputation: 303517

When you inherit from Drawable:

class SierpinskiTri : public sf::Drawable { .. };

you also inherit all of its methods, one of which is:

virtual void draw (RenderTarget &target, RenderStates states) const = 0;

You are not providing an implementation of draw, so your SierpinksiTri class is also an abstract class and you cannot create an instance of an abstract class.

The solution is to provide an implementation for draw().

Upvotes: 3

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