[C++知识库]C++学习记录（2）——运算符重载

2021.11.23

类和对象之运算符重载

1.加法运算符重载

class Person
{
public:
	Person() {};        //默认构造函数，用于后面定义Person temp;
	Person(int a, int b)
	{
		m_A = a;
		m_B = b;
	}
	//Person operator+(Person &p)		//成员函数实现加法重载
	//{
	//	Person temp;
	//	temp.m_A = this->m_A + p.m_A;
	//	temp.m_B = this->m_B + p.m_B;
	//	return temp;
	//}
	int m_A, m_B;
};
//全局函数实现加法重载
Person operator+(Person &p1, Person &p2)
{
	Person temp;
	temp.m_A = p1.m_A + p2.m_A;
	temp.m_B = p1.m_B + p2.m_B;
	return temp;
}
Person operator+(Person &p1, int num)
{
	Person temp;
	temp.m_A = p1.m_A + num;
	temp.m_B = p1.m_B + num;
	return temp;
}
//调用
    Person p1(10, 10);
	Person p2(10, 10);
	成员函数重载本质为：Person p3 = p1.operator+(p2);
	全局函数重载本质为：Person p3 = operator+(p1,p2);
	Person p3 = p1 + p2;
	Person p4 = p1 + 100;

2.左移运算符重载

ostream& operator<<(ostream &out, Person &p)        //类代码与上述代码相似
{
	out << "m_A= " << p.m_A << "\tm_B=" << p.m_B;
	return out;
}
//调用
    cout << p << endl;

3.递增运算符重载

class MyInit {
	friend ostream& operator<<(ostream& out, MyInit myinit);
public:
	MyInit() {
		m_Num = 0;
	}
	MyInit& operator++()		//前置运算符，++a，先加后赋值
	{
		m_Num++;
		return *this;
	}
	MyInit operator++(int)		//后置运算符，a++，先赋值再++
	{                           //这里用占位参数，让编译器知道作后置递增
		MyInit temp;
		temp = *this;
		m_Num++;
		return temp;
	}
private:
	int m_Num;
};
//调用
    MyInit myinit;
	cout << ++(++myinit) << endl;
    cout << myinit++ << endl;

这里进行cout输出需要用到上一部分的左移重载

4.赋值运算符重载

class Person{
public:
	Person(int age) {
		m_Age = new int(age);
	}
	~Person() {
		if (m_Age != NULL)
		{
			delete m_Age;
			m_Age = NULL;
		}
	}
	Person& operator=(Person& p) {
		if (m_Age != NULL)		//先判断是否有属性在堆区，如果有先释放，然后再进行深拷贝
		{
			delete m_Age;
			m_Age = NULL;
		}
		m_Age = new int(*p.m_Age);
		return *this;
	}
	int *m_Age;
};
//调用
    Person p1(18);
	Person p2(20);
	Person p3(25);
	p3 = p2 = p1;

5.关系运算符重载

class Person {
public:
	Person(string name, int age) {
		m_Name = name;
		m_Age = age;
	}
	bool operator==(Person &p) {
		if (this->m_Name == p.m_Name && this->m_Age == p.m_Age)
		{
			return true;
		}
		else
		{
			return false;
		}
	}
	string m_Name;
	int m_Age;
};
//调用
    Person p1("张三", 18);
	Person p2("lisi", 18);
	if (p1 == p2)  {  }
	else   {   }

6.函数调用运算符重载

函数调用运算符()也可以重载，由于重载后使用的方式非常像函数的调用，因此称为仿函数。

class MyAdd
{
public:
	int operator()(int a, int b) {
		return a + b;
	}
};
//调用
    MyAdd myadd;
	int res = myadd(100,100);
//匿名对象调用
    cout << MyAdd()(100, 100) << endl;