1.友元函数方式为类重载运算符

（友元函数声明可以放在类任何地方）

1.类

class MM {
public:
	MM() {}
	MM(int grade,string name):grade(grade),name(name){}
	friend MM operator+(MM object1, MM object2);
	void print() {
		cout << this->grade << this->name << endl;
	}
private:
	int grade;
	string name;
};

2.重载运算符函数编写

MM operator+(MM object1, MM object2) {
	MM object;
	object.grade = (object1.grade + object2.grade) / 2;
	object.name = object1.name;
	return object;
}

3.main

int main() {
	MM object1(60,"小王");
	MM object2(80, "小王");
	MM object3 = object1 + object2;
	object3.print();
	return 0;
}

结果：

2.使用成员函数实现重载运算符（使用this来减少传参）

1.class

class MM {
public:
	MM() {}
	MM(int grade,string name):grade(grade),name(name){}
	MM operator+(MM object1);
	void print() {
		cout << this->grade << this->name << endl;
	}
private:
	int grade;
	string name;
};

2.实现函数

MM MM::operator+(MM object1) {
	MM object;
	object.grade = (object1.grade + this->grade) / 2;
	object.name = this->name;
	return object;
}

3.main

int main() {
	MM object1(60,"小王");
	MM object2(80, "小王");
	MM object3 = object1 + object2;
	object3.print();
	return 0;
}

结果：

3.对象的前置后置++

1.class

class MM {
public:
	MM() {}
	MM(int size2, string name) :size2(size2), name(name) {}
	MM& operator++();
	MM& operator++(int);
	void print() {
		cout << this->name << "是" << size1 << "位用户，size2=" << this->size2 << endl;
	}
private:
	static int size1;
	int size2=0;
	string name;
};
int MM::size1 =0;

2.实现函数

（1）前置

MM& MM::operator++() {//前置++
	this->size1++;
	this->size2++;
	return (*this);
}

精简版：

MM& MM::operator++() {//前置++
	this->size++;
	return (*this);
}

（2）后置

MM& MM::operator++(int) {//后置++
	MM *object=new MM;
	object->name = this->name;
	object->size1 = this->size1;
	object->size2 = this->size2;
	this->size1++;this->size2++;
	return *object;
}

精简版：

MM& MM::operator++(int) {//后置++
	MM *object=new MM;
	object->size = this->size;
	this->size++;
	return *object;
}

3.main

int main() {
	//前置++
	MM mm1(10, "小爱");
	++mm1;
	mm1.print();
	//后置++
	MM mm2(10, "小洁");
	MM mm3=mm2++;//重点：实现函数中*object是赋值mm3
	mm3.print();//10
	mm2.print();//11
	return 0;
}

结果：