C++类与对象之运算符重载详解 C++类与对象之运算符重载详解

运算符重载
加号运算符重载
左移运算符重载
递增运算符重载
递减运算符重载
赋值运算符重载
关系运算符重载
函数调用运算符重载
总结

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
【C++类与对象之运算符重载详解】
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

#include using namespace std; class Person {public: // 构造函数 Person(int num1, int num2){this->num1 = num1; this->num2 = num2; } // 加法函数 Person operator+(const Person &p){Person temp(0, 0); temp.num1 = this->num1 + p.num1; temp.num2 = this->num2 + p.num2; return temp; } // 打印输出 void printMessage() {cout << "num1 = " << num1 << " num2 = " << num2 << endl; }private: int num1; int num2; }; void func() { Person p1(1, 2); Person p2(3, 4); Person p3 = p1.operator+(p2); // 可以简化为 Person = p1 + p2; p3.printMessage(); // num1 = 4 num2 = 6 Person p4 = p3 + p2; p4.printMessage(); // num1 = 7 num2 = 10}int main() { func(); system("pause"); return 0; }

左移运算符重载作用：输出自定义数据类型
第一种：成员函数（对象 << cout）

#include using namespace std; class Person {public: // 构造函数 Person(int num1, int num2){this->num1 = num1; this->num2 = num2; } // 左移运算符 p.operator<<(cout); 简化版本 p << cout void operator <<(ostream &cout) {cout << "num1 = " << num1 << " num2 = " << num2 << endl; }private: int num1; int num2; }; void func() { Person p1(1, 2); p1.operator<<(cout); // 简化为 p1 << cout Person p2(3, 4); p2 << cout; }int main() { func(); // outputs:num1 = 1 num2 = 2 //num1 = 3 num2 = 4 system("pause"); return 0; }

第二种：全局函数（cout << 对象）

#include using namespace std; class Person { // 友元 friend ostream& operator <<(ostream &cout, Person &p); public: // 构造函数 Person(int num1, int num2){this->num1 = num1; this->num2 = num2; }private: int num1; int num2; }; // 左移运算符 p.operator<<(cout); 简化版本 p << coutostream& operator <<(ostream &cout, Person &p) { cout << "num1 = " << p.num1 << " num2 = " << p.num2; return cout; }void func() { Person p1(1, 2); operator<<(cout, p1); // 简化为 cout << p1; cout << endl; cout << p1 << " 你是猪！" << endl; }int main() { func(); // outputs:num1 = 1 num2 = 2 //num1 = 1 num2 = 2 你是猪！ system("pause"); return 0; }

递增运算符重载通过重载递增运算符，实现自己的整型数据

#include using namespace std; class MyInteger { //friend ostream& operator <<(ostream &cout, MyInteger &p); friend ostream& operator <<(ostream &cout, MyInteger p); public: // 构造函数 MyInteger(){this->m_num = 0; } // 重载前置递增运算符 MyInteger& operator++() {++this->m_num; return *this; } // 重载后置递增运算符 MyInteger operator++(int) { // int 是占位参数，用于区分前置和后置递增MyInteger temp = *this; ++this->m_num; return temp; }private: int m_num; }; // 用于前置递增，左移运算符 p.operator<<(cout); 简化版本 p << cout//ostream& operator <<(ostream &cout, MyInteger &p) {// cout << "m_num = " << p.m_num; // return cout; //}// 用于后置递增，左移运算符 p.operator<<(cout); 简化版本 p << coutostream& operator <<(ostream &cout, MyInteger p) { cout << "m_num = " << p.m_num; return cout; }void func() { MyInteger m_int; //cout << m_int.operator++() << endl; // m_num = 1 //cout << ++m_int << endl; // m_num = 2 cout << m_int++ << endl; // m_num = 0 cout << m_int << endl; // m_num = 1}int main() { func(); system("pause"); return 0; }

递减运算符重载通过重载递减运算符，实现自己的整型数据

#include using namespace std; class MyInteger { friend ostream& operator <<(ostream &cout, MyInteger &p); //friend ostream& operator <<(ostream &cout, MyInteger p); public: // 构造函数 MyInteger(){this->m_num = 0; } // 重载前置递减运算符 MyInteger& operator--() {--this->m_num; return *this; } // 重载后置递减运算符 MyInteger operator--(int) { // int 是占位参数，用于区分前置和后置递增MyInteger temp = *this; --this->m_num; return temp; }private: int m_num; }; // 用于前置递减，左移运算符 p.operator<<(cout); 简化版本 p << coutostream& operator <<(ostream &cout, MyInteger &p) { cout << "m_num = " << p.m_num; return cout; }// 用于后置递减，左移运算符 p.operator<<(cout); 简化版本 p << cout//ostream& operator <<(ostream &cout, MyInteger p) {// cout << "m_num = " << p.m_num; // return cout; //}void func() { MyInteger m_int; cout << m_int.operator--() << endl; // m_num = -1 cout << --m_int << endl; // m_num = -2 //cout << m_int-- << endl; // m_num = 0 //cout << m_int << endl; // m_num = -1}int main() { func(); system("pause"); return 0; }

赋值运算符重载 C++ 编译器至少给一个类添加 4 个函数（此处不举例，具体可见核心篇 5）

#include using namespace std; class Student {public: // 构造函数 Student(int id) {m_id = new int(id); // 从堆区开辟内存用来存储 id } // 拷贝构造函数 Student(const Student &s) {this->m_id = new int(*s.m_id); } // 析构函数 ~Student() {if (m_id != NULL) {delete m_id; m_id = NULL; } } // 重载赋值运算符 Student& operator=(Student &s) {if (m_id != NULL) {delete m_id; m_id = NULL; }m_id = new int(*s.m_id); return *this; } // 取出 id int getId() {return *m_id; }private: int *m_id; }; void func() { Student s1(1); cout << s1.getId() << endl; // 1 // 用拷贝构造函数来作深拷贝 Student s2(s1); cout << s2.getId() << endl; // 1 // 用赋值重载运算符来作赋值 Student s3(2); // id 为 2 s1 = s3; // 复杂版本：s1.operator=(s3) cout << s1.getId() << endl; // 2 // 多段赋值运算符，例如 a = b = c Student s4(3); s1 = s2 = s3 = s4; // id 均为 3 cout << s1.getId() << s2.getId() << s3.getId() << s4.getId() << endl; // 3333}int main() { func(); system("pause"); return 0; }

关系运算符重载重载关系运算符，可以让两个自定义数据类型对象进行对比操作

#include using namespace std; class Student {public: // 构造函数 Student(int id) {m_id = new int(id); // 从堆区开辟内存用来存储 id } // 拷贝构造函数 Student(const Student &s) {this->m_id = new int(*s.m_id); } // 析构函数 ~Student() {if (m_id != NULL) {delete m_id; m_id = NULL; } } // 重载 == 运算符 bool operator==(Student &s) {if (this->getId() == s.getId()) {return true; }else {return false; } } // 取出 id int getId() {return *m_id; }private: int *m_id; }; void func() { Student s1(1); Student s2(1); Student s3(2); if (s1 == s2) {cout << "s1 和 s2 相等" << endl; } if (s1 == s3) {cout << "s1 和 s3 相等" << endl; } else {cout << "s1 和 s3 不相等" << endl; }}int main() { func(); // outputs:s1 和 s2 相等 //s1 和 s3 不相等 system("pause"); return 0; }

函数调用运算符重载特点：函数调用运算符 () 也可以重载；重载后调用的方式很像函数，被称为仿函数；没有固定写法，非常灵活

#include using namespace std; #include class Print {public: void operator()(string text) {cout << "利用函数调用重载运算符打印输出：" << text << endl; }}; void func() { Print p1; p1("你是一个小猪猪！"); // 利用函数调用重载运算符打印输出：你是一个小猪猪！}int main() { func(); // outputs:s1 和 s2 相等 //s1 和 s3 不相等 system("pause"); return 0; }

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