运算符重载

1.重载’+'运算符

为什么要重载加法运算符？

因为C++提供的加法运算符只能满足基本数据类型间的加法，如果我想让俩个相同的类的对象进行加法的话会报错

所以为了能让俩个相同类的对象进行加法，我们要把这个过程封装到一个函数里面，只不过要多加一个关键字operator而已，让编译器一下子就找到，这个是重载运算符的函数

作用：实现俩个自定义运算符相加

成员函数实现运算符重载

可以少传递一个参数

#include <iostream>

using namespace std;

class Box {
	int length;
	int width;
	int height;
public:
	Box() {
		length = 0;
		width = 0;
		height = 0;
	}
	Box(int length,int width,int height) {
		this->length = length;
		this->width = width;
		this->height = height;
	}
	Box(const Box& other) {
		length = other.length;
		width = other.width;
		height = other.height;
	}
	//成员函数重载加法运算符
	Box operator+(const Box& other) {
		Box p;
		p.length = this->length + other.length;
		p.width = this->width + other.width; 
		p.height = this->height + other.height;
		return p;
	}
};
int main() {
	Box a(1,2,3);
	Box b(2, 3, 4);
	Box c = a + b;//直接调用
	Box d;
	d = a.operator+(b);//调用重载运算符的函数
	return 0;
}

全局函数实现运算符的重载

#include <iostream>

using namespace std;

class Box {
	int length;
	int width;
	int height;
	friend Box operator+(const Box& other1, const Box& other2);
	friend Box operator+(const Box& other1, int val);
public:
	Box() {
		length = 0;
		width = 0;
		height = 0;
	}
	Box(int length,int width,int height) {
		this->length = length;
		this->width = width;
		this->height = height;
	}
	Box(const Box& other) {
		length = other.length;
		width = other.width;
		height = other.height;
	}
};
//全局函数重载加法运算符
Box operator+(const Box& other1,const Box& other2) {//不调用成员函数是无法访问私有的成员变量的，需要设置为友元，告诉编译器，我这个重载运算符的函数是你这个类的好朋友，都哥们，能f
	Box p;
	p.length = other1.length + other2.length;
	p.width = other1.width + other2.width;
	p.height = other1.height + other2.height;
	return p;
}
Box operator+(const Box& other1,int val) {
	Box p;
	p.length = other1.length + val;
	p.width = other1.width + val;
	p.height = other1.height + val;
	return p;
}
int main() {
	Box a(1,2,3);
	Box b(2, 3, 4);
	Box c = a + b;
	Box d;
	d=operator+(a,b);
	return 0;
}

2.重载’+=’ 运算符

#include <iostream>

using namespace std;
class Box {
	int length;
	int width;
	int high;
	friend Box& operator+=(Box& other1, Box& other2);
public:
	Box() {
		length = 1;
		width = 2;
		high = 3;
	}
	/*Box& operator+=(const Box& other) {
		this->length += other.length;
		this->width += other.width;
		this->high += other.high;
		return *this;
	}*/
	int get_length() {
		return this->length;
	}
};
Box& operator+=(Box& other1,Box& other2) {
	other1.length += other2.length;
	other1.width += other2.width;
	other1.high += other2.high;
	return other1;
}
int main() {
	Box a, b,c;
	a += b+=c;//隐式调用函数
	cout << a.get_length();
	return 0;
}

3.重载’<<'运算符

cout是ostream类的对象

cin是istream类的对象

#include <iostream>

using namespace std;
class Box {
	int length;
	int width;
	int high;
	friend ostream& operator<<(ostream& o, const Box& b);
public:
	Box() {
		length = 1;
		width = 2;
		high = 3;
	}
};
ostream& operator<<(ostream& o,const Box& b) {
	o << b.length << ' ' << b.width << ' ' << b.high << endl;
	return o;
}
int main() {
	Box a, b,c;
	//cout << a;没有与这些操作数相匹配的运算符
	/*
	* 你想重载一个运算符要么在类内重载，要么在类外重载
	* 但是cout对象属于ostream类，该类我们无法修改，所以只能在类外用全局函数重载
	*/
	cout << a << b << c;
	return 0;
}

4.重载’>>'运算符

#include <iostream>

using namespace std;
class Box {
	int length;
	int width;
	int high;
	friend ostream& operator<<(ostream& o, const Box& b);
	friend istream& operator>>(istream& i, Box& b);
public:
	Box() {
		length = 1;
		width = 2;
		high = 3;
	}
};
ostream& operator<<(ostream& o,const Box& b) {
	o << b.length << ' ' << b.width << ' ' << b.high << endl;
	return o;
}
istream& operator>>(istream& i,Box& b) {
	i >> b.length;
	i >> b.width;
	i >> b.high;
	return i;
}
int main() {
	Box a, b,c;
	//cout << a;没有与这些操作数相匹配的运算符
	/*
	* 你想重载一个运算符要么在类内重载，要么在类外重载
	* 但是cout对象属于ostream类，该类我们无法修改，所以只能在类外用全局函数重载
	*/
	cin >> a>>b>>c;
	cout << a << b << c;
	return 0;
}