C++类的组合实例

主程序

#include "pch.h"
#include "Line.h"

/*//函数声明
void fun1(Point p);
Point fun2();*/

int main()
{
	Point myp1(1, 1), myp2(4, 5);    //建立Point类的对象
	Line line(myp1, myp2);           //建立Line类的对象
	cout << "==================================================" << endl;
	Line line2(line);                //利用拷贝构造函数建立一个新对象
	cout << "The length of the line is : "
		<< line.getLen() << endl;
	cout << "The length of the line is : "
		<< line2.getLen() << endl;
	return 0;
}

pch.h文件

#ifndef PCH_H
#define PCH_H
#include 
using namespace std;

class Point
{
public:
	Point();
	Point(int, int);
	Point(const Point &);
	virtual ~Point();

	int Getx() { return x; }
	int Gety() { return y; }

protected:

private:
	int x;
	int y;
};
#endif //PCH_H

pch.cpp

#include "pch.h"

Point::Point():x(1), y(2)
{

}
Point::Point(int _x, int _y)
{
	x = _x; y = _y;
}
Point::Point(const Point &p)
{
	x = p.x;
	y = p.y;
	cout << "Calling the copy constructor of Point!" << endl;
}
Point::~Point()
{
	//dtor
}

Line.h

#pragma once
class Line
{
public:
	Line();
	Line(Line &);      //复制构造函数声明
	Line(Point, Point);//组合类构造函数声明
	double getLen() { return len; }
	~Line();
private:
	Point p1, p2;
	int len;
};

Line.cpp

#include "pch.h"
#include "line.h"


Line::Line():p1(1, 1),p2(2, 3)
{
}

//拷贝构造函数
Line::Line(Line &L):p1(L.p1),p2(L.p2)
{
	cout << "Calling the copy constructor of Line !" << endl;
	len = L.len;
}

//组合类构造函数
Line::Line(Point _p1, Point _p2) :p1(_p1), p2(_p2)
{
	cout << "Calling constructor of Line !" << endl;
	double x = static_cast<double>(p1.Getx() - p2.Getx());
	double y = static_cast<double>(p1.Gety() - p2.Gety());
	len = sqrt(x * x + y * y);
}

Line::~Line()
{
}

运行结果如下（可使用单步调试查看程序具体运行过程，进行理解）：