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
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 <iostream>
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 <iostream>
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 <iostream>
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 << cout
ostream& 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 <iostream>
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 << 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;
}
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 <iostream>
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 << cout
ostream& 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 <iostream>
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 <iostream>
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 <iostream>
using namespace std;
#include <string>
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;
}
总结
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