派生类中的默认构造函数

Question

我正在读我的旧考试去学习决赛,并注意到一些我仍然不理解的东西.

class Shape
{
  private:
  int center_x, int center_y;
  public:
  Shape (int x, int y) : center_x(x), center_y(y); {} //constructor initializer
}
class Rectangle : public Shape
{
  private:
  int length, width;
  public:
  Rectangle(): //this is where i have trouble, I am supposed to fill in missing code here
  //but shape does not have a default constructor, what am i supposed to fill in here?
  Rectangle (int x, int y, int l, int w) : Shape(x,y);{length = l; width = w;}
}

谢谢

Answer 1

有两种方法.您可以在默认构造函数的mem-initializer列表中调用基类construcor,并使用一些默认值(例如,我使用零作为默认值):

Rectangle() : Shape( 0, 0 ), length( 0 ), width( 0 ) {}

或者,您可以将默认构造函数中的所有工作委托给带参数的构造函数.

例如

Rectangle() : Rectangle( 0, 0, 0, 0 ) {}

考虑到类定义应以分号结束.:)