A类继承了B类，在A构造函数时不能A（B m,B n）吗？

Question

#include <stdafx.h>
#include <iostream.h>
#include <math.h>
class CPoint
{
public:
CPoint(double a,double b){x=a;y=b;}
double getx(){return x;}
double gety(){return y;}
void show()
{cout<<x<<","<<y<<endl;}
private:
double x,y;
};
class CLine:public CPoint
{
private:
CPoint p1,p2;
public:
CLine(CPoint a,CPoint b) //提示是这里出错
{
p1=a;
p2=b;
}
double length()
{
return sqrt(pow(p1.getx()-p2.getx(),2)+pow(p1.gety()-p2.gety(),2));
}
};
void main()
{
CPoint p1(0,0);
CPoint p2(5,0);
p1.show();
cout<<"to"<<endl;
p2.show();
CLine l1(p1,p2);
cout<<"length="<<l1.length()<<endl;
}

Answer 1

不是这个问题，是你的CPoint类的构造函数都要求有参数。
在CPoint中增加一个不需要参数的构造函数就OK了