运算符重载
运算符重载概念：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
一.加号运算符重载
作用：实现两个自定义数据类型相加的运算
class Person { public: Person() {}; Person(int a, int b) { this->m_A = a; this->m_B = b; } //成员函数实现 + 号运算符重载 Person operator+(const Person& p) { Person temp; temp.m_A = this->m_A + p.m_A; temp.m_B = this->m_B + p.m_B; return temp; } public: int m_A; int m_B; }; //全局函数实现 + 号运算符重载 //Person operator+(const Person& p1, const Person& p2) { // Person temp(0, 0); // temp.m_A = p1.m_A + p2.m_A; // temp.m_B = p1.m_B + p2.m_B; // return temp; //} //运算符重载 可以发生函数重载 Person operator+(const Person& p2, int val) { Person temp; temp.m_A = p2.m_A + val; temp.m_B = p2.m_B + val; return temp; } void test() { Person p1(10, 10); Person p2(20, 20); //成员函数方式 Person p3 = p2 + p1; //相当于 p2.operaor+(p1) cout << "mA:" << p3.m_A << " mB:" << p3.m_B << endl; Person p4 = p3 + 10; //相当于 operator+(p3,10) cout << "mA:" << p4.m_A << " mB:" << p4.m_B << endl; } int main() { test(); system("pause"); return 0; }
总结1：对于内置的数据类型的表达式的的运算符是不可能改变的
总结2：不要滥用运算符重载
二.左移运算符重载
作用：可以输出自定义数据类型
class Person { friend ostream& operator<<(ostream& out, Person& p); public: Person(int a, int b) { this->m_A = a; this->m_B = b; } //成员函数 实现不了 p << cout 不是我们想要的效果 //void operator<<(Person& p){ //} private: int m_A; int m_B; }; //全局函数实现左移重载 //ostream对象只能有一个 ostream& operator<<(ostream& out, Person& p) { out << "a:" << p.m_A << " b:" << p.m_B; return out; } void test() { Person p1(10, 20); cout << p1 << "hello world" << endl; //链式编程 } int main() { test(); system("pause"); return 0; }
总结：重载左移运算符配合友元可以实现输出自定义数据类型
三.递增运算符重载
作用： 通过重载递增运算符，实现自己的整型数据
class MyInteger { friend ostream& operator<<(ostream& out, MyInteger myint); public: MyInteger() { m_Num = 0; } //前置++ MyInteger& operator++() { //先++ m_Num++; //再返回 return *this; } //后置++ MyInteger operator++(int) { //先返回 MyInteger temp = *this; //记录当前本身的值，然后让本身的值加1，但是返回的是 以前的值，达到先返回后++； m_Num++; return temp; } private: int m_Num; }; ostream& operator<<(ostream& out, MyInteger myint) { out << myint.m_Num; return out; } //前置++ 先++ 再返回 void test01() { MyInteger myInt; cout << ++myInt << endl; cout << myInt << endl; } //后置++ 先返回 再++ void test02() { MyInteger myInt; cout << myInt++ << endl; cout << myInt << endl; } int main() { test01(); //test02(); system("pause"); return 0; }
总结： 前置递增返回引用，后置递增返回值
四.赋值运算符重载
c++编译器至少给一个类添加4个函数
1. 默认构造函数(无参，函数体为空)
2. 默认析构函数(无参，函数体为空)
3. 默认拷贝构造函数，对属性进行值拷贝
4. 赋值运算符 operator=, 对属性进行值拷贝
如果类中有属性指向堆区，做赋值操作时也会出现深浅拷贝问题
示例：
class Person { public: Person(int age) { //将年龄数据开辟到堆区 m_Age = new int(age); } //重载赋值运算符 Person& operator=(Person &p) { if (m_Age != NULL) { delete m_Age; m_Age = NULL; } //编译器提供的代码是浅拷贝 //m_Age = p.m_Age; //提供深拷贝 解决浅拷贝的问题 m_Age = new int(*p.m_Age); //返回自身 return *this; } ~Person() { if (m_Age != NULL) { delete m_Age; m_Age = NULL; } } //年龄的指针 int *m_Age; }; void test01() { Person p1(18); Person p2(20); Person p3(30); p3 = p2 = p1; //赋值操作 cout << "p1的年龄为：" << *p1.m_Age << endl; cout << "p2的年龄为：" << *p2.m_Age << endl; cout << "p3的年龄为：" << *p3.m_Age << endl; } int main() { test01(); //int a = 10; //int b = 20; //int c = 30; //c = b = a; //cout << "a = " << a << endl; //cout << "b = " << b << endl; //cout << "c = " << c << endl; system("pause"); return 0; }
五.关系运算符重载
作用：重载关系运算符，可以让两个自定义类型对象进行对比操作
示例：
class Person { public: Person(string name, int age) { this->m_Name = name; this->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; } } bool operator!=(Person & p) { if (this->m_Name == p.m_Name && this->m_Age == p.m_Age) { return false; } else { return true; } } string m_Name; int m_Age; }; void test01() { //int a = 0; //int b = 0; Person a("孙悟空", 18); Person b("孙悟空", 18); if (a == b) { cout << "a和b相等" << endl; } else { cout << "a和b不相等" << endl; } if (a != b) { cout << "a和b不相等" << endl; } else { cout << "a和b相等" << endl; } } int main() { test01(); system("pause"); return 0; }
六.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
仿函数没有固定写法，非常灵活
示例：
class MyPrint { public: void operator()(string text) { cout << text << endl; } }; void test01() { //重载的（）操作符 也称为仿函数 MyPrint myFunc; myFunc("hello world"); } class MyAdd { public: int operator()(int v1, int v2) { return v1 + v2; } }; void test02() { MyAdd add; int ret = add(10, 10); cout << "ret = " << ret << endl; //匿名对象调用 cout << "MyAdd()(100,100) = " << MyAdd()(100, 100) << endl; } int main() { test01(); test02(); system("pause"); return 0; }
