C++ C+中的抽象类错误+；SFML

大家好，我想尝试制作一个Sierpinski三角形会是一个有趣的练习，我对这个抽象类错误有一个问题，我似乎无法解决。当我试图创建一个SierpinskiTri“SierpinskiTri-sierpinskiii；”对象，然后将其绘制到窗口“window.draw（sierpinskiii）；”时，我在该对象上得到一个错误，说它是一个抽象类

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);
}


};

当您继承自：

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);
}


};

您还可以继承其所有方法，其中之一是：

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);
}


};

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

您没有提供

draw

的实现，因此您的

SierpinksiTri

类也是一个抽象类，您无法创建抽象类的实例

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);
}


};

解决方案是为

draw（）

提供一个实现

当您继承自：

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);
}


};

您还可以继承其所有方法，其中之一是：

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);
}


};

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

您没有提供

draw

的实现，因此您的

SierpinksiTri

类也是一个抽象类，您无法创建抽象类的实例

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);
}


};

解决方案是为

draw（）

提供一个实现

您必须覆盖该功能：

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);
}


};

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

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

您已经编写了该函数：

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);
}


};

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

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

结果，派生类是抽象的，就像编译器所说的那样。为了重写，您需要正确匹配虚拟函数的签名

您必须覆盖该功能：

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);
}


};

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

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

您已经编写了该函数：

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);
}


};

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

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

结果，派生类是抽象的，就像编译器所说的那样。为了重写，您需要正确匹配虚拟函数的签名

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);
}


};