[C++核心编程]（七）：类和对象——运算符重载*

目录

四则运算符重载

左移运算符重载

递增运算符重载

赋值运算符重载

关系运算符重载

函数调用运算符重载

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对已有的运算符重新进行定义，赋予其另一种功能，以适应不同的数据类型

四则运算符重载

        对自定义数据类型实现四则运算（加减乘除）操作，比如：自己写成员函数，实现两个对象相加属性后返回新的对象

        注意：四则运算符重载也可以进行函数重载。

        总结：

        1.对于内置的数据类型的表达式的的运算符是不可以改变的

        2.不要滥用运算符重载

#include <iostream>using namespace std;class Person
{
public:int m_a;int m_b;Person(int a, int b) :m_a(a), m_b(b){}//成员函数重载Person operator+(const Person &p){Person rp(0, 0);rp.m_a = this->m_a + p.m_a;rp.m_b = this->m_b + p.m_b;return rp;}
};
//全局函数重载
static Person operator-(const Person& p1, const Person& p2)
{Person rp(0, 0);rp.m_a = p1.m_a - p2.m_a;rp.m_b = p1.m_b - p2.m_b;return rp;
}
//函数重载
static Person operator-(const Person& p1, const int value)
{Person rp(0, 0);rp.m_a = p1.m_a - value;rp.m_b = p1.m_b - value;return rp;
}int main(void)
{Person p1(10, 10);Person p2(10, 10);Person p3(5, 5);Person p4 = p1 + p2; //Person p4 = p1.operator+(p2);cout << "p4 m_a value:" << p4.m_a << endl;cout << "p4 m_b value:" << p4.m_b << endl;Person p5 = p4 - p3; //Person p5 = operator-(p4,p3)cout << "p5 m_a value:" << p5.m_a << endl;cout << "p5 m_b value:" << p5.m_b << endl;Person p6 = p5 - 5; //Person p6 = operator-(p5,5)cout << "p6 m_a value:" << p6.m_a << endl;cout << "p6 m_b value:" << p6.m_b << endl;system("pause");return 0;
}

左移运算符重载

        输出自定义的数据类型，比如：直接输出一个对象就可以输出其成员属性

        总结：左移运算符配合友元可以实现输出自定义数据类型

#include <iostream>
#include <string>using namespace std;class Person
{friend static ostream& operator<<(ostream& cout, Person& p);
public:Person(int a, int b){m_a = a;m_b = b;}
private://通常不使用 成员函数重载 左移运算符 ,无法实现cout在左侧int m_a;int m_b;
};static ostream& operator<<(ostream &cout, Person& p) // operator<<(cout, p)
{cout << "m_a=" << p.m_a << endl;cout << "m_b=" << p.m_b << endl;return cout;
}static void test(void)
{Person p(10, 10);cout << p << endl;
}int main(void)
{test();system("pause");return 0;
}

递增运算符重载

        区分前置和后置的差别！！

#include <iostream>
#include <string>using namespace std;class MyInteger
{friend static ostream& operator<<(ostream& cout, MyInteger p);
public:MyInteger(int b){m_b = b;}//重载 后置,int 占位参数 int ，区分前置和后置MyInteger operator++(int){MyInteger temp = *this;++*this;return temp;}//重载 前置MyInteger& operator++() //返回引用是为了一直对一个数据进行操作{++m_b;return *this;}
private:int m_b;
};static ostream& operator<<(ostream& cout, MyInteger p) // operator<<(cout, p)
{cout << p.m_b;return cout;
}static void test(void)
{MyInteger p(0);cout << ++p << endl;cout << p << endl;
}static void test1(void)
{MyInteger p1(0);cout << p1++ << endl;cout << p1 << endl;
}int main(void)
{test();test1();system("pause");return 0;
}

赋值运算符重载

         c++至少给一个类添加4个函数：前三个略

        4.赋值运算符operator=，对属性进行值拷贝（注意深浅拷贝问题）

#include <iostream>
#include <string>using namespace std;class Person
{
public:Person(int b){m_age = new int(b);}~Person(){if (m_age != NULL){delete m_age;m_age = NULL;}}Person& operator=(const Person & p) //重载赋值运算符,使用深拷贝{if (m_age != NULL){delete m_age;m_age = NULL;}m_age = new int(*p.m_age);return *this;}int *m_age;
};static void test1(void)
{Person p1(12);Person p2(19);Person p3(14);p3 = p2 = p1;cout << "p1年龄为：" << *p1.m_age << endl;cout << "p2年龄为：" << *p2.m_age << endl;cout << "p3年龄为：" << *p3.m_age << endl;
}int main(void)
{test1();system("pause");return 0;
}

关系运算符重载

        重载关系运算符，让两个自定义的数据类型进行对比操作

#include <iostream>
#include <string>using namespace std;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;
};static void test1(void)
{Person p1("Tom", 19);Person p2("Mac", 19);if (p1 == p2){cout << "p1 == p2" << endl;}else{cout << "p1 != p2" << endl;}}int main(void)
{test1();system("pause");return 0;
}

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，故称仿函数
• 仿函数没有固定写法，非常灵活（返回值、参数均不固定）

#include <iostream>
#include <string>using namespace std;class Myprint
{
public:void operator()(string test){cout << test << endl;}
};class MyAdd
{
public:int operator()(int a, int b){return a + b;}
};static void test1(void)
{Myprint myprint;myprint("Hello World!");//仿函数MyAdd myadd;int result = myadd(1, 1);cout << "result = " << result << endl;//匿名函数对象cout << "result = " << MyAdd()(11, 11) << endl;
}int main(void)
{test1();system("pause");return 0;
}

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