这篇文章主要讲解了“c++友元与运算符重载怎么应用”,文中的讲解内容简单清晰,易于学习与理解,下面请大家跟着小编的思路慢慢深入,一起来研究和学习“C++友元与运算符重载怎么应用”吧!友元生活中你的家有客厅(Public),有你的卧室(Pri
这篇文章主要讲解了“c++友元与运算符重载怎么应用”,文中的讲解内容简单清晰,易于学习与理解,下面请大家跟着小编的思路慢慢深入,一起来研究和学习“C++友元与运算符重载怎么应用”吧!
生活中你的家有客厅(Public),有你的卧室(Private),客厅所有来的客人都可以进去,但是你的卧室是私有的,也就是说只有你能进去,但是呢,你也可以允许你的好闺蜜好基友进去。
在程序里,有些私有属性也想让类外特殊的一些函数或者类进行访问,就需要用到友元的技术。
友元的目的就是让一个函数或者类访问另一个类中私有成员。
友元的关键字为: friend
友元的三种实现:
全局函数做友元
类做友元
成员函数做友元
class Building{//告诉编译器 GoodGay全局函数 是 Building类的好朋友,可以访问类中的私有内容friend void goodGay(Building * building);public:Building(){this->m_SittingRoom = "客厅";this->m_BedRoom = "卧室";}public:string m_SittingRoom; //客厅private:string m_BedRoom; //卧室};void goodGay(Building * building){cout << "好基友正在访问: " << building->m_SittingRoom << endl;cout << "好基友正在访问: " << building->m_BedRoom << endl;}void test01(){Building b;goodGay(&b);}int main(){test01();system("pause");return 0;}
class Building;class goodGay{public:goodGay();void visit();private:Building *building;};class Building{//告诉编译器 goodGay类是Building类的好朋友,可以访问到Building类中私有内容friend class goodGay;public:Building();public:string m_SittingRoom; //客厅private:string m_BedRoom;//卧室};Building::Building(){this->m_SittingRoom = "客厅";this->m_BedRoom = "卧室";}goodGay::goodGay(){building = new Building;}void goodGay::visit(){cout << "好基友正在访问" << building->m_SittingRoom << endl;cout << "好基友正在访问" << building->m_BedRoom << endl;}void test01(){goodGay gg;gg.visit();}int main(){test01();system("pause");return 0;}
class Building;class goodGay{public:goodGay();void visit(); //只让visit函数作为Building的好朋友,可以发访问Building中私有内容void visit2(); private:Building *building;};class Building{//告诉编译器 goodGay类中的visit成员函数 是Building好朋友,可以访问私有内容friend void goodGay::visit();public:Building();public:string m_SittingRoom; //客厅private:string m_BedRoom;//卧室};Building::Building(){this->m_SittingRoom = "客厅";this->m_BedRoom = "卧室";}goodGay::goodGay(){building = new Building;}void goodGay::visit(){cout << "好基友正在访问" << building->m_SittingRoom << endl;cout << "好基友正在访问" << building->m_BedRoom << endl;}void goodGay::visit2(){cout << "好基友正在访问" << building->m_SittingRoom << endl;//cout << "好基友正在访问" << building->m_BedRoom << endl;}void test01(){goodGay gg;gg.visit();}int main(){test01();system("pause");return 0;}
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
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
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
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
c++编译器至少给一个类添加4个函数
默认构造函数(无参,函数体为空)
默认析构函数(无参,函数体为空)
默认拷贝构造函数,对属性进行值拷贝
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;}
**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;}
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;}
感谢各位的阅读,以上就是“C++友元与运算符重载怎么应用”的内容了,经过本文的学习后,相信大家对C++友元与运算符重载怎么应用这一问题有了更深刻的体会,具体使用情况还需要大家实践验证。这里是编程网,小编将为大家推送更多相关知识点的文章,欢迎关注!
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