C++類與對(duì)象之運(yùn)算符重載詳解

更新時(shí)間：2021年10月18日 09:55:55 作者：是我來晚了！

運(yùn)算符重載的方法是定義一個(gè)重載運(yùn)算符的函數(shù)，在需要執(zhí)行被重載的運(yùn)算符時(shí)，系統(tǒng)就自動(dòng)調(diào)用該函數(shù)，以實(shí)現(xiàn)相應(yīng)的運(yùn)算。也就是說，運(yùn)算符重載是通過定義函數(shù)實(shí)現(xiàn)的

運(yùn)算符重載

運(yùn)算符重載概念：對(duì)已有的運(yùn)算符重新進(jìn)行定義，賦予其另一種功能，以適應(yīng)不同的數(shù)據(jù)類型

加號(hào)運(yùn)算符重載

作用：實(shí)現(xiàn)兩個(gè)自定義數(shù)據(jù)類型相加的運(yùn)算

#include <iostream>
using namespace std;
class Person {
public:
	// 構(gòu)造函數(shù)
	Person(int num1, int num2){
		this->num1 = num1;
		this->num2 = num2;
	}
	// 加法函數(shù)
	Person operator+(const Person &p){
		Person temp(0, 0);
		temp.num1 = this->num1 + p.num1;
		temp.num2 = this->num2 + p.num2;
		return temp;
	}
	// 打印輸出
	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); // 可以簡化為 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;
}

左移運(yùn)算符重載

作用：輸出自定義數(shù)據(jù)類型

第一種：成員函數(shù)（對(duì)象 << cout）

#include <iostream>
using namespace std;
class Person {
public:
	// 構(gòu)造函數(shù)
	Person(int num1, int num2){
		this->num1 = num1;
		this->num2 = num2;
	}
	// 左移運(yùn)算符 p.operator<<(cout); 簡化版本 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); // 簡化為 p1 << cout
	Person p2(3, 4);
	p2 << cout;
}
int main() {
	func();
	// outputs:num1 = 1 num2 = 2
	//		   num1 = 3 num2 = 4
	system("pause");
	return 0;
}

第二種：全局函數(shù)（cout << 對(duì)象）

#include <iostream>
using namespace std;
class Person {
	// 友元
	friend ostream& operator <<(ostream &cout, Person &p);
public:
	// 構(gòu)造函數(shù)
	Person(int num1, int num2){
		this->num1 = num1;
		this->num2 = num2;
	}
private:
	int num1;
	int num2;
};
// 左移運(yùn)算符 p.operator<<(cout); 簡化版本 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); // 簡化為 cout << p1;
	cout << endl;
	cout << p1 << " 你是豬！" << endl;
}
int main() {
	func();
	// outputs:num1 = 1 num2 = 2
	//		   num1 = 1 num2 = 2 你是豬！
	system("pause");
	return 0;
}

遞增運(yùn)算符重載

通過重載遞增運(yùn)算符，實(shí)現(xiàn)自己的整型數(shù)據(jù)

#include <iostream>
using namespace std;
class MyInteger {
	//friend ostream& operator <<(ostream &cout, MyInteger &p);
	friend ostream& operator <<(ostream &cout, MyInteger p);
public:
	// 構(gòu)造函數(shù)
	MyInteger(){
		this->m_num = 0;
	}
	// 重載前置遞增運(yùn)算符
	MyInteger& operator++() {
		++this->m_num;
		return *this;
	}
	// 重載后置遞增運(yùn)算符
	MyInteger operator++(int) { // int 是占位參數(shù)，用于區(qū)分前置和后置遞增
		MyInteger temp = *this;
		++this->m_num;
		return temp;
	}
private:
	int m_num;
};
// 用于前置遞增，左移運(yùn)算符 p.operator<<(cout); 簡化版本 p << cout
//ostream& operator <<(ostream &cout, MyInteger &p) {
//	cout << "m_num = " << p.m_num;
//	return cout;
//}
// 用于后置遞增，左移運(yùn)算符 p.operator<<(cout); 簡化版本 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;
}

遞減運(yùn)算符重載

通過重載遞減運(yùn)算符，實(shí)現(xiàn)自己的整型數(shù)據(jù)

#include <iostream>
using namespace std;
class MyInteger {
	friend ostream& operator <<(ostream &cout, MyInteger &p);
	//friend ostream& operator <<(ostream &cout, MyInteger p);
public:
	// 構(gòu)造函數(shù)
	MyInteger(){
		this->m_num = 0;
	}
	// 重載前置遞減運(yùn)算符
	MyInteger& operator--() {
		--this->m_num;
		return *this;
	}
	// 重載后置遞減運(yùn)算符
	MyInteger operator--(int) { // int 是占位參數(shù)，用于區(qū)分前置和后置遞增
		MyInteger temp = *this;
		--this->m_num;
		return temp;
	}
private:
	int m_num;
};
// 用于前置遞減，左移運(yùn)算符 p.operator<<(cout); 簡化版本 p << cout
ostream& operator <<(ostream &cout, MyInteger &p) {
	cout << "m_num = " << p.m_num;
	return cout;
}
// 用于后置遞減，左移運(yùn)算符 p.operator<<(cout); 簡化版本 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;
}

賦值運(yùn)算符重載

C++ 編譯器至少給一個(gè)類添加 4 個(gè)函數(shù)（此處不舉例，具體可見核心篇 5）

#include <iostream>
using namespace std;
class Student {
public:
	// 構(gòu)造函數(shù)
	Student(int id) {
		m_id = new int(id); // 從堆區(qū)開辟內(nèi)存用來存儲(chǔ) id
	}
	// 拷貝構(gòu)造函數(shù)
	Student(const Student &s) {
		this->m_id = new int(*s.m_id);
	}
	// 析構(gòu)函數(shù)
	~Student() {
		if (m_id != NULL) {
			delete m_id;
			m_id = NULL;
		}
	}
	// 重載賦值運(yùn)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
	// 用拷貝構(gòu)造函數(shù)來作深拷貝
	Student s2(s1);
	cout << s2.getId() << endl; // 1
	// 用賦值重載運(yùn)算符來作賦值
	Student s3(2); // id 為 2
	s1 = s3; // 復(fù)雜版本：s1.operator=(s3)
	cout << s1.getId() << endl; // 2
	// 多段賦值運(yùn)算符，例如 a = b = c
	Student s4(3);
	s1 = s2 = s3 = s4; // id 均為 3
	cout << s1.getId() << s2.getId() << s3.getId() << s4.getId() << endl; // 3333
}
int main() {
	func();
	system("pause");
	return 0;
}

關(guān)系運(yùn)算符重載

重載關(guān)系運(yùn)算符，可以讓兩個(gè)自定義數(shù)據(jù)類型對(duì)象進(jìn)行對(duì)比操作

#include <iostream>
using namespace std;
class Student {
public:
	// 構(gòu)造函數(shù)
	Student(int id) {
		m_id = new int(id); // 從堆區(qū)開辟內(nèi)存用來存儲(chǔ) id
	}
	// 拷貝構(gòu)造函數(shù)
	Student(const Student &s) {
		this->m_id = new int(*s.m_id);
	}
	// 析構(gòu)函數(shù)
	~Student() {
		if (m_id != NULL) {
			delete m_id;
			m_id = NULL;
		}
	}
	// 重載 == 運(yùn)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;
}

函數(shù)調(diào)用運(yùn)算符重載

特點(diǎn)：函數(shù)調(diào)用運(yùn)算符 () 也可以重載；重載后調(diào)用的方式很像函數(shù)，被稱為仿函數(shù)；沒有固定寫法，非常靈活

#include <iostream>
using namespace std;
#include <string>
class Print {
public:
	void operator()(string text) {
		cout << "利用函數(shù)調(diào)用重載運(yùn)算符打印輸出：" << text << endl;
	}
};
void func() {
	Print p1;
	p1("你是一個(gè)小豬豬！"); // 利用函數(shù)調(diào)用重載運(yùn)算符打印輸出：你是一個(gè)小豬豬！
}
int main() {
	func();
	// outputs:s1 和 s2 相等
	//		   s1 和 s3 不相等
	system("pause");
	return 0;
}