C++特殊成员详解

#include<iostream>
#include<string>
using namespace std;
class king{
public:
	king(int data) :num(data)//初始化参数列表初始化数据
	{
		cout << num << endl;
	}
	void print()const//常成员函数
	{
		cout << "hello!" << endl;
	}
	void printdata()//普通函数
	{
		str = "lijue";
		cout << str << endl;
	}
protected:
	string str;
	const int num;//常数据成员
};
int main(){
	king prince(18);
	prince.print();//普通对象调用常成员函数
	const king boy(12);
	boy.print();//常对象调用常成员函数
	while (1);
	return 0;
}

//普通友元函数，可以打破权限的限制
#include<iostream>
using namespace std;
void print();
class myfriend{
public:
protected:
	int data = 150;
	friend void print(myfriend&k){
		cout << k.data << endl;
	}
};
int main(){
	myfriend k;
	print(k);
	while (1);
	return 0;
}

//以另一个类的成员函数充当友元函数
#include<iostream>
using namespace std;
class myfriend;
class I{
public:
	void print();
protected:
};
class myfriend{
public:
	friend void I::print();
protected:
	int data = 150;		
};
void I::print()
{
	myfriend k;
	cout << k.data << endl;
}
int main(){
	I K;
    K.print();
	while (1);
	return 0;
}

//友元类
#include<iostream>
using namespace std;
class A;
class B{
public:
	friend class A;
protected:
	int data = 123;
};
class A{
public:
	void printData()
   {
		B l;
		cout << l.data << endl;
   }
protected:
       };
int main()
{
	A l;
	l.printData();
	while (1);
	return 0;
}