C++非成员函数、友元函数、重载运算符

#ifndef MYCLASS_H
#define MYCLASS_H

#include 
using namespace std;

class MyClass
{
    friend bool operator==(int b, MyClass my); //友元函数重载运算符

    friend void sayHello(MyClass my); //友元函数

public:
    bool operator==(int b){return (b == a);} //成员函数重载运算符

private:
    int a;

public:
    enum Hello{hello = 0, world};

public:
    MyClass();
};

void sayHello(); //非成员函数

#endif // MYCLASS_H

cpp文件

#include 
#include "myclass.h"

using namespace std;

bool operator==(int b, MyClass my)
{
    return (b == my.a);
}

void sayHello(MyClass my)
{
    cout << "a:" << my.a << endl;
}

void sayHello()
{
    cout << "Hello World" << endl;
}


MyClass::MyClass():a(2)
{
}

main.cpp

#include 
#include "myclass.h"

using namespace std;

int main()
{
    cout << "Hello World!" << endl;

    MyClass my, you;
    bool c = (3 == you);

    cout << "c:" << c << endl;

    cout << "my==2:" << (my==2) << endl;

    sayHello(my);

    sayHello();

    return 0;
}