关于C++，如果把a(x1,y1);b(x2,y2);c(x3,y3)写在花括号里就是错误，但如果写成参数化表就不错，why?

public:p(double x1,double y1){x=x1;y=y1,double y3):p(x,y){a(x1,y1);b(x2:double x;double y,double x3;a# includeusing namespace std;c(x3,y3);};};int main(){v a(15,16:public p{protected:p a;p b;p c;public,double x2.display();class p{protected,45);x<}};<,1,double x1,double y2,19,19;class v,y2),double y1:void display(){a.display();b.display();c.display();}v(double x,double y;}void display(){cout<;