友元函数
- 友元函数和友元类（破坏类的封装性）
- 面向对象编程思想
#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cmath>
using namespace std;
class Point;
class PointManager {
public:
double PointDistance(Point &p1, Point &p2);
};
class Point
{
public:
//声明全局函数 PointDistance 是我类Point类的一个友元函数。
//friend double PointDistance(Point &p1, Point &p2);
friend double PointManager::PointDistance(Point &p1, Point &p2);
Point(int x, int y) {
this->x = x;
this->y = y;
}
int getX()
{
return this->x;
}
int getY()
{
return this->y;
}
private:
int x;
int y;
};
double PointManager::PointDistance(Point &p1, Point &p2)
{
double dis;
int dd_x = p1.x - p2.x;
int dd_y = p1.y - p2.y;
dis = sqrt(dd_x*dd_x + dd_y *dd_y);
return dis;
}
# if 0
double PointDistance(Point &p1, Point &p2)
{
double dis;
int dd_x = p1.x - p2.x;
int dd_y = p1.y - p2.y;
dis = sqrt(dd_x*dd_x + dd_y *dd_y);
return dis;
}
#endif
int main(void)
{
Point p1(1, 2);
Point p2(2, 2);
//cout << PointDistance(p1, p2) << endl;
PointManager pm;
cout << pm.PointDistance(p1, p2) << endl;
return 0;
}
友元类
#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
using namespace std;
class A
{
public:
A(int a)
{
this->a = a;
}
void printA() {
cout << "a = " << this->a << endl;
// B objB(3000);
// cout << objB.b << endl;
}
//声明一个友元类B
friend class B;
private:
int a;
};
class B
{
public:
B(int b)
{
this->b = b;
}
void printB() {
A objA(100);
cout << objA.a << endl;
cout << "b = " << this->b << endl;
}
friend class A;
private:
int b;
};
int main(void)
{
B bObj(200);
bObj.printB();
return 0;
}