#include <iostream>
using namespace std;
class A {
friend class B; //类B是类A的友元
public:
static int value;
static int num;
A(int x, int y) {
xp = x, yp = y;
value++;
cout << "调用构造:" << value << endl;
}
void displayA() {
cout << xp << "，" << yp << endl;
}
~A() {
num++;
cout << "调用析构:" << num << endl;
}
private:
int xp, yp;
};
class B {
public:
B(int x1, int x2) : mpt1(x1 + 2, x2 - 2), mpt2(x1, x2) {
cout << "调用构造\n"; //mpt是类A的对象，有几个mpt，有关类A的操作便执行几次
}
void set(int m, int n);
void displayB();
~B() {
cout << "调用析构\n"; //析构函数在类结束前调用，类结束的时候释放类申请的空间
}
private:
A mpt1, mpt2; //将A类的对象声明为B类的私有数据成员
};
int A::value = 0;
int A::num = 0;
void B::set(int m, int n) {
mpt1.xp = m * 2, mpt1.yp = n / 2;
}
void B::displayB() {
mpt1.displayA();
}
int main() {
B p(10, 20);
cout << "Hello world!" << endl;
B displayB(); //通过友元，使类B输出类A的私有数据成员
return 0;
}
