[C++知识库]C++运算符重载

友元函数重载运算符

1.运算符重载：赋予运算符具有操作自定义类型数据功能

2.运算符重载的实质是函数调用

函数返回值类型? ? ?函数名(函数参数)

（1）函数返回值类型：运算完成后的值决定的? ? ? ? ? ? ? ??

（2）函数名：operator 加上重载运算符组成函数名

（3）参数：看运算符的操作数,具体参数个数是要看你重载函数形式是什么

（4）函数体：写运算符具体想要的操作

3.友元函数重载和类成员函数重载（参数个数少一）

类成员函数重载运算符

#include <iostream>
#include <string>
using namespace std;
class A
{
public:
	A(int a=0,int b=0):a(a), b(b){}
	friend A operator+ (A one, A two);
	void print()
	{
		cout << a << "\t" << b << endl;
	}
	bool operator>(A two)
	{
		if (this->a > two.a || (this->a == two.a&&this->b > two.b))
			return true;
		else
			return false;
	}
protected:
	int a;
	int b;
};
A operator+(A one, A two)
{
	return A(one.a + two.a, one.b + two.b);
}
int main()
{
	A one(2, 1);
	A two(1, 0);
	A three = one + two;//three=operator+(A one,A two);显示调用
	three.print();
	if (one > two/*one.operator>(two)*/)
	{
		cout << "one 大" << endl;
	}
	return 0;
}

特殊运算符重载

1.流运算符重载

（1）cin类型：istream类的对象

（2）cout类型：ostream类的对象

（3）流运算符? <<? ?>>

（4）必须采用友元函数形式重载

#include <iostream>
#include <string>
using namespace std;
class Boy
{
public:
	Boy(string name="", int age=0) :name(name), age(age){}
	friend istream& operator>>(istream& in, Boy& boy);
	friend ostream& operator<<(ostream& out, Boy& boy);
protected:
	string name;
	int age;
};
istream& operator>>(istream& in, Boy& boy)
{
	in >> boy.name>>boy.age;
	return in;
}
ostream& operator<<(ostream& out, Boy& boy)
{
	out << boy.name << "\t" << boy.age << endl;
	return out;
}
int main()
{
	string name;
	cin >> name;
	cout << name << endl;
	Boy boy;
	cin >> boy;             //void operator>>(istream& in,Boy& boy);
	cout << boy << endl;    //void operator<<(ostream& out,Boy& boy);
	cin >> name >> boy;
	cout << name << "\t" << boy;
	return 0;
}

2.++--运算符重载

（1）前置后置：增加无用参数int表示后置操作

3.文本重载

4.其他运算符

（1）=? ()? ->? [ ]? 只能采用类的成员函数形式重载

（2）流重载采用友元方式

（3）.? ? ?.*? ? ??:? ? ::不能重载

5.类的隐式对象的转换

#include <iostream>
#include <string>
using namespace std;
class Boy
{
public:
	Boy(string name, int age) :name(name), age(age){}
	friend ostream& operator<<(ostream& out, Boy& boy)
	{
		out << boy.name << "\t" << boy.age;
		return out;
	}
	Boy operator++(int)//后置
	{
		return Boy(name, age++);
	}
	Boy operator++()
	{
		return Boy(name, ++age);
	}
	Boy operator--(int)
	{
		return Boy(name, age--);
	}
	Boy operator--()
	{
		return Boy(name, --age);
	}
protected:
	string name;
	int age;
};
int main()
{
	Boy boy("name", 21);
	Boy boy1 = boy++;
	cout << boy1 << "\t" << boy << endl;
	boy1 = ++boy;
	cout << boy1 << "\t" << boy << endl;
	return 0;
}