https://www.cnblogs.com/nanzh/p/7994811.html
Line类调用Point类的两个对象p1,p2作为其数据成员，计算线段长度
组合类构造函数定义的一般形式为：
类名::类名(形参表):内嵌对象1(形参表),内嵌对象2(形参表)...
{类的初始化}
Line例子（课本例子学习）：
1 #include<iostream>
2 #include<cmath>
3 using namespace std;
4 class Point{
5 public:
6 //隐式内联构造函数（显示inline）
7 Point(int newX,int newY){
8 x=newX;
9 y=newY;
10 }
11 //复制构造函数
12 Point(Point &p);
13 int getX(){return x;}
14 int getY(){return y;}
15 private:
16 int x,y;
17
18 };
19 //复制构造函数的实现
20 Point::Point(Point &p){
21 x=p.x;
22 y=p.y;
23 }
24
25 //类的组合
26 class Line{
27 public:
28 Line(Point xp1,Point xp2);
29 Line(Line &q);
30 double getLen(){return len;}
31 private:
32 Point p1,p2;
33 double len;
34 };
35 //组合类的构造函数
36 Line::Line(Point xp1,Point xp2):p1(xp1),p2(xp2){
37 double x=static_cast<double>(p1.getX()-p2.getX());
38 double y=static_cast<double>(p1.getY()-p2.getY());
39 len=sqrt(x*x+y*y);
40 }
41 //组合类的复制构造函数
42 Line::Line(Line &q):p1(q.p1),p2(q.p2){
43 cout<<"calling the copy construct of Line"<<endl;
44 len=q.len;
45 }
46
47 void fun1(Point p){
48 cout<<"fun1:"<<p.getX()<<","<<p.getY()<<endl;
49 }
50 Point fun2(){
51 Point a(1,2);
52 return a;
53 }
54 int main(){
55 //Point
56 Point a(8,9);
57 Point b=a;
58 cout<<"test point:x="<<b.getX()<<endl;
59 fun1(b);
60 b=fun2();
61 cout<<"test point:x="<<b.getX()<<endl;
62 //Line
63 //point类的复制构造函数被调用了6次
64 //两个对象在Line构造函数进行函数参数形实参结合时+初始化内嵌对象时+复制构造line2时被调>用
65 cout<<"------------"<<endl;
66 Point m(3,4),n(5,6);
67 Line line(m,n);
68 cout<<"line:"<<line.getLen()<<endl;
69 Line line2(line);
70 cout<<"line2:"<<line2.getLen()<<endl;
71
72 return 0;
73 }
运行结果Ubuntu下g++编译：
