C++友元与运算符重载结合友元

Posted 2021-12-18 程序彤

友元

1.全局函数做友元

#include <iostream>

using namespace std;

/**
 * 全局函数做友元
 */
class Building 
    friend void coming(Building *building);

public:
    string sittingRoom;

    Building() 
        this->sittingRoom = "客厅";
        livingRoom = "卧室"; // 省略this->
    

private:
    string livingRoom;
;

// Building中并未声明coming()函数，故此为类外全局函数。
void coming(Building *building) 
    cout << "同性正在访问" << building->sittingRoom << endl;
    // 如果不用friend声明友元函数则无法访问私有成员变量
    cout << "同性正在访问" << building->livingRoom << endl; // friend



void test01() 
    Building building;
    coming(&building);


int main() 
    test01();
    return 0;

2.友元类>友元函数，功能相同，需权限处登记

#include <iostream>

using namespace std;


class Building; // 必须声明

class Gay 
    // 谁是谁的朋友，友元类到底声明在哪里？-反正不是这里，你需要去权限掌控者处登记。
public:
    Gay();

    void visit();

    void visit2();

private:
    Building *building; // 开局不声明，这里则报错
;

class Building 
    // 必须在我Building这里登记
//    friend class Gay; // 正确，友元类
    friend void Gay::visit(); // 这里切记必须Gay的成员函数先声明！！Building和Gay调换位置则失效！！

public:
    string sittingRoom;

    Building();

private:
    string livingRoom;
;

Gay::Gay() 
    building = new Building; // 这里的小building在类外居然可以访问，牛逼🐂。


void Gay::visit() 
    cout << "Gay正在访问" << building->sittingRoom << endl;
    cout << "Gay正在访问" << building->livingRoom << endl;


// 类外Building的构造函数
Building::Building() 
    this->sittingRoom = "客厅";
    this->livingRoom = "卧室";


void Gay::visit2() 
    cout << "Gay正在访问" << building->sittingRoom << endl;
//    cout << "Gay正在访问" << building->livingRoom << endl; // visit2()无权限访问livingRoom


void test1() 
    Gay gay;
    gay.visit();
    gay.visit2();


int main() 
    test1();
    return 0;

运算符重载（全局/成员运算符重载）

1.加号运算符重载

p1+p2，等同于Person p3 = p1.operator+(p2);

2.左移运算符重载（结合全局函数友元）

#include <iostream>

using namespace std;

class Liweitong 
    // 在此处注册登记
    friend ostream &operator<<(ostream &cout, Liweitong &liweitong);

public:
    Liweitong();

private:
    string name;
    int age;
;

// 全局构造函数
Liweitong::Liweitong() 
    name = "weton";
    age = 23;


// 全局左移运算符重载函数
ostream &operator<<(ostream &cout, Liweitong &liweitong) 
    // 这里的name和age为私有属性,若想在全局函数中访问，使用友元
    cout << "name=" << liweitong.name << " age=" << liweitong.age << endl;
    return cout;


void test1() 
    Liweitong liweitong;
    cout << liweitong << endl;


int main() 
    test1();
    return 0;

3.递增运算符重载

// 递增运算符重载
class MyInt 
    friend ostream &operator<<(ostream &out, MyInt myInt);

public:
    MyInt() 
        num = 0;
    

    // 前置++
    MyInt &operator++() 
        num++;
        return *this;
    

    // 后置++
    MyInt operator++(int) 
        MyInt myIntTemp = *this;
        num++;
        return myIntTemp;
    

private:
    int num;
;

ostream &operator<<(ostream &out, MyInt myInt) 
    out << "num=" << myInt.num;
    return out;


void test1() 
    Liweitong liweitong;
    cout << liweitong << endl;


void test2() 
    MyInt myInt;
    cout << ++myInt << endl;
    cout << myInt << endl;


void test3() 
    MyInt myInt;
    cout << myInt++ << endl;
    cout << myInt << endl;



int main() 
    test1(); // 全局左移运算符重载 =tostring()
    printf("-------------------\\n");
    test2(); // 前置++
    printf("-------------------\\n");
    test3(); // 后置++
    return 0;

4.赋值运算符重载

class Li 
public:
    Li(int tmpAge) 
        age = new int(tmpAge);
    

    ~Li()   // 此时报错error for object 0x7fe26b704080: pointer being freed was not allocated
        if (age !=NULL)
            delete age;
            age = NULL;
        
    

    // 使用赋值运算符重载解决报错问题
    Li& operator=(Li &li)
        if (age!=NULL)
            delete age;
            age = NULL;
        
        age = new int(*li.age);
        return *this;
    
    int *age; // int指针类型
;

void test1() 
    Liweitong liweitong;
    cout << liweitong << endl;


void test2() 
    MyInt myInt;
    cout << ++myInt << endl;
    cout << myInt << endl;


void test3() 
    MyInt myInt;
    cout << myInt++ << endl;
    cout << myInt << endl;



void test4() 
    Li l1(10);
    Li l2(20);
    Li l3(30);
    l3 = l2 = l1;
    cout << *l1.age << endl; //10
    cout << *l2.age << endl; //10
    cout << *l3.age << endl; //10

5.关系运算符重载

class Guanxi 
public:
    string name;
    int age;

    Guanxi(string name, int age) 
        this->name = name;
        this->age = age;
    

    bool operator==(Guanxi &guanxi) 
        if (this->name == guanxi.name && this->age == guanxi.age) 
            return true;
        
        return false;
    
;

6.函数调用运算符重载

仿函数

//函数调用运算符重载
class MyPrint 
public:
    void operator()(string text) 
        cout << text << endl;
    
;

class MyAdd
public:
    int operator()(int n1,int n2)
        return n1+n2    ;
    
;
void test1() 
    Liweitong liweitong;
    cout << liweitong << endl;


void test2() 
    MyInt myInt;
    cout << ++myInt << endl;
    cout << myInt << endl;


void test3() 
    MyInt myInt;
    cout << myInt++ << endl;
    cout << myInt << endl;



void test4() 
    Li l1(10);
    Li l2(20);
    Li l3(30);
    l3 = l2 = l1;
    cout << *l1.age << endl; //10
    cout << *l2.age << endl; //10
    cout << *l3.age << endl; //10


void test5() 
    Guanxi g1("lwt", 23);
    Guanxi g2("lwt", 22);
    if (g1 == g2)  // 如果不声明关系运算符重载，则这里编译不通过
        cout << "两对象相等" << endl;
        return;
    
    cout << "两对象不相等!!!" << endl;


// 函数调用运算符重载
void test6()
    MyPrint myPrint;
    myPrint.operator()("void operator()(string text)...");
    MyAdd myAdd;
    int res = myAdd.operator()(1,3);
    printf("%d\\n",res);

int main() 
    test1(); // 全局左移运算符重载 =tostring()
    printf("-------------------\\n");
    test2(); // 前置++  递增运算符重载
    printf("-------------------\\n");
    test3(); // 后置++
    printf("-------------------\\n");
    test4(); // 赋值运算符重载
    printf("-------------------\\n");
    test5(); // 关系运算符重载==
    printf("-------------------\\n");
    test6(); //

    return 0;



void test5() 
    Guanxi g1("lwt", 23);
    Guanxi g2("lwt", 22);
    if (g1 == g2)  // 如果不声明关系运算符重载，则这里编译不通过
        cout << "两对象相等" << endl;
        return;
    
    cout << "两对象不相等!!!" << endl;