non-virtual interface(NVI)手法:令用户通过public non-virtual成员函数间接调用private virtual函数,将这个non-virtual函数称为virtual函数的wrapper.wrapper确保得以在一个virtual函数被调用之前设定好适当场景,并在调用结束之后清理场景.注意此时用指针或引用调用该non-virtual成员函数时,该non-virtual成员函数调用的virtual函数取决于指针或引用的动态类型,即存在多态
enum ShapeColor { Red, Green, Blue };
class Shape
{
public:
void draw(ShapeColor color = Red) const
{
doDraw(color);
}
private:
virtual void doDraw(ShapeColor color) const = 0;
};
class Rectangle :public Shape
{
public:
private:
virtual void doDraw(ShapeColor color) const;
};
void Rectangle::doDraw(ShapeColor color) const
{
cout << "Rectangle's doDraw" << "color= " << color << endl;
}
void main()
{
Shape*p = new Rectangle;
////输出:Rectangle's doDrawcolor= 0
p->draw();
system("pause");
}
enum ShapeColor { Red, Green, Blue };
class Shape
{
public:
void draw(ShapeColor color = Red)const
{
doDraw(color);
}
private:
virtual void doDraw(ShapeColor color) const
{
cout << "Shape's doDraw" << "color= " << color << endl;
}
};
class Rectangle :public Shape
{
public:
private:
virtual void doDraw(ShapeColor color) const;
};
void Rectangle::doDraw(ShapeColor color) const
{
cout << "Rectangle's doDraw" << "color= " << color << endl;
}
/*
输出:
Shape's doDrawcolor= 0
Rectangle's doDrawcolor= 0
*/
void main()
{
Shape*p = new Shape;
p->draw();
delete p;
p = NULL;
Shape*q = new Rectangle;
q->draw();
delete q;
q = NULL;
system("pause");
}
enum ShapeColor { Red, Green, Blue };
class Shape
{
public:
void draw(ShapeColor color = Red)const
{
doDraw(color);
}
private:
void doDraw(ShapeColor color) const
{
cout << "Shape's doDraw" << "color= " << color << endl;
}
};
class Rectangle :public Shape
{
public:
private:
void doDraw(ShapeColor color) const;
};
void Rectangle::doDraw(ShapeColor color) const
{
cout << "Rectangle's doDraw" << "color= " << color << endl;
}
/*
输出:
Shape's doDrawcolor= 0
Shape's doDrawcolor= 0
*/
int main()
{
Shape*p = new Shape;
p->draw();
delete p;
p = NULL;
Shape*q = new Rectangle;
q->draw();
delete q;
q = NULL;
system("pause");
return 0;
}
原文链接: https://www.cnblogs.com/ljygoodgoodstudydaydayup/p/5813163.html
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