【C++】运算符重载

对已有的运算符重新定义

一、加号重载

本质是Student s3=s1.operator+(s2);

（一）使用成员函数重载

class Student {
public:
	int a;
	int b;
	Student operator+(Student& p) {
		Student t;
		t.a = this->a + p.a;
		t.b = this->b + p.b;
	}
};

（二）使用全局变量重载

本质调用：Student s3=operator+(s1，s2);

Student operator+(Student &s,Student &s1) {
	Student t;
	t.a =s.a + s1.a;
	t.b = s.b + s1.b;
	return t;
}

运算符重载也可以发生函数重载

Student operator+(Student &s,int s1) {
	Student t;
	t.a =s.a + s1;
	t.b = s.b + s1;
	return t;
}

二、左移<<重载

不会利用成员函数重载<<运算符，因为无法实现cout在左侧
使用全局变量重载
如果想用类中的私有变量加友元：friend ostream& operator<<(ostream& cout, Student& s);
cout和out关键字属于输出流ostream

ostream& operator<<(ostream& cout, Student& s) {
	cout << "a=" << s.a << "\tb=" << s.b;
	//链式
	return cout;
}
ostream& operator<<(ostream& out, Student& s) {
	out << "a=" << s.a << "\tb=" << s.b;
	//链式
	return out;
}
void test() {
	Student s1(10,20);	
	cout << s1 << endl;
}

三、递增符号重载

class Student {
	friend ostream& operator<<(ostream& cout, Student& s);
public:
	int a;
	int b;
	Student() {
		a = 0;
	}
	//重载前置++
	Student& operator++() {
		//先加
		a++;
		//再返回自身
		return *this;
	}

	//后置++,int是占位参数，区分前置后后置
	Student& operator++(int) {
		//先记录结果
		Student t = *this;
		//后递增
		a++;
		//将记录返回
		return t;
	}
};
ostream& operator<<(ostream& out, Student& s) {
	out << s.a ;
	//链式
	return out;
}
void test() {
	Student s;
	cout << ++(++s) << endl;
	cout << s << endl;
}
void test1() {
	Student s;
	cout << s++ << endl;
	cout << s << endl;
}

四、赋值符重载

可以看看构造函数和析构函数深拷贝和浅拷贝：深拷贝和浅拷贝

class Student {
public:
	int *a;
	Student(int _a) {
		a = new int(_a);
	}
	~Student() {
		if (a != NULL) {
			delete a;
			a = NULL;
		}
	}
	Student& operator=(Student& s) {
		//编译器提供浅拷贝
		//先判断是否有属性在堆区，如果有先释放干净，再深拷贝
		if (a != NULL) {
			delete a;
			a = NULL;
		}
		a = new int(*s.a);

		//返回对象本身
		return *this;

	}
};
void test() {
	Student s(18);
	Student s1(20);
	Student s2(23);
	cout << "年龄" << *s.a << endl;
	s2 = s1=s;
	cout << "年龄" << *s1.a << endl;
	cout << "年龄" << *s2.a << endl;
}

关系运算符重载

bool operator!=(Student& s) {
		if (this->a != s.a && this->b != s.b) {
			return true;
		}
		return false;
	}

函数调用运算符重载（）

1、函数调用运算符()也可以重载
2、由于重载后使用的方法非常像函数的调用，因此成为仿函数
3、仿函数没有固定写法，非常灵活

class Student {
public:
	int a;
	int b;
	//打印输出函数重载
	void operator()(string test) {
		cout << test << endl;
	}
	//两个数相加
	int operator()(int num1, int n2) {
		return num1 + n2;
	}
};
void test() {
	Student s;
	s("World");
	cout << s(18, 20) << endl;
	int ret = s(10, 10);
	cout << ret << endl;
	//匿名函数对象
	cout << Student()(10, 10) << endl;
	
}