[C++] Operator overloading ④ (Unary operator overloading | Use global functions to implement prefix ++ auto-increment operator overloading | Use global functions to implement prefix - - Auto-decrement operator overloading)

1. Unary operator overloading

---

1. List of unary operators

Unary operator: also known as unary operator

• Negation operator: -
• Dereference operator: *
• Get address operator: &
• Auto-increment operator: ++ , this operator is divided into two types: prefix and postfix;
• Decrement operator: – , this operator is divided into two types: prefix and postfix;

2. Implement operator overloading operations for the following classes

In this blog, the unary operator overloading operation is implemented for the following Student class;

class Student
{
    
    
public:
	// 带参构造函数 , 为参数设置默认值
	Student(int age = 1, int height = 1)
	{
    
    
		this->age = age;
		this->height = height;
	};

public:
	// 打印类数据
	void print()
	{
    
    
		cout << "age = " << age << " , height = " << height << endl;
	};

public:
	// 使用 成员函数 实现 运算符重载 
	// 重载 - 运算符
	// 实现两个 Student 对象相加
	Student operator-(Student& s)
	{
    
    
		Student student(this->age - s.age, this->height - s.height);
		return student;
	};

private:
	int age;		// 年龄
	int height;		// 身高
};

3. Use global functions to implement prefix ++ auto-increment operator overloading

Use global functions to implement prepended ++ increment operator overloading:

• First, write the function name. The function name rule is "operate" followed by the operator to be overloaded . The function name is operate++;

operate++

• Then, write the function parameters according to the operands, and the parameters are generally references to objects;
  • Member function: The parameter is$A$ constant reference to an object, such as:operate+(const Student& s1)
  • Global function: parameters are$References\; to\; 2$ objects, such as:operate+(Student& s1, Student& s2)

operator++(Student& s)

• Then, according to the business improvement of the return value, the return value can be a reference/pointer/element, such as: the return value is an element Student operate+(Student& s1, Student& s2); here, because the attributes in the Student& s parameter have changed, the Student& s parameter still needs to be returned when returning. itself, so the return value is Student& reference type;

Student& operator++(Student& s)

• Finally, implement the function body and write specific operators to operate the business logic;

// 使用 全局函数 实现 前置 ++ 自增运算符重载
// 重载 前置 ++ 运算符
// 实现 1 个 Student 对象 自增运算
// 由于 参数中的 Student& s 中的属性发生了变化 
// 返回时仍需要返回 Student& s 参数本身
Student& operator++(Student& s)
{
    
    
	s.age++;
	s.height++;
	return s;
};

In order to enable the global function to access the private members of the Student class, the global function needs to be declared as a friend function;

	// 使用 全局函数 实现 前置 ++ 自增运算符重载
	friend Student& operator++(Student& s);

4. Use global functions to implement prepositioning - overloading of decrement operators

Use global functions to implement prefix--decrement operator overloading:

• First, write the function name. The function name rule is "operate" followed by the operator to be overloaded . The function name is operate--;

operate--

• Then, write the function parameters according to the operands, and the parameters are generally references to objects;
  • Member function: The parameter is$A$ constant reference to an object, such as:operate+(const Student& s1)
  • Global function: parameters are$References\; to\; 2$ objects, such as:operate+(Student& s1, Student& s2)

operator--(Student& s)

• Then, according to the business improvement of the return value, the return value can be a reference/pointer/element, such as: the return value is an element Student operate+(Student& s1, Student& s2); here, because the attributes in the Student& s parameter have changed, the Student& s parameter still needs to be returned when returning. itself, so the return value is Student& reference type;

Student& operator--(Student& s)

• Finally, implement the function body and write specific operators to operate the business logic;

// 使用 全局函数 实现 前置 -- 自减运算符重载
// 重载 前置 -- 运算符
// 实现 1 个 Student 对象 自减运算
// 由于 参数中的 Student& s 中的属性发生了变化 
// 返回时仍需要返回 Student& s 参数本身
Student& operator--(Student& s)
{
    
    
	s.age--;
	s.height--;
	return s;
};

In order to enable the global function to access the private members of the Student class, the global function needs to be declared as a friend function;

	// 使用 全局函数 实现 前置 -- 自增运算符重载
	friend Student& operator--(Student& s);

2. Complete code example

---

Code example:

#include "iostream"
using namespace std;

class Student
{
    
    
public:
	// 带参构造函数 , 为参数设置默认值
	Student(int age = 1, int height = 1)
	{
    
    
		this->age = age;
		this->height = height;
	};

public:
	// 打印类数据
	void print()
	{
    
    
		cout << "age = " << age << " , height = " << height << endl;
	};

public:
	// 使用 成员函数 实现 运算符重载 
	// 重载 - 运算符
	// 实现两个 Student 对象相加
	Student operator-(Student& s)
	{
    
    
		Student student(this->age - s.age, this->height - s.height);
		return student;
	};

private:
	// 友元函数 实现 全局函数 运算符重载
	// 使用 全局函数 实现 + 运算符重载 
	friend Student operator+(Student& s1, Student& s2);

	// 使用 全局函数 实现 前置 ++ 自增运算符重载
	friend Student& operator++(Student& s);

	// 使用 全局函数 实现 前置 -- 自增运算符重载
	friend Student& operator--(Student& s);

private:
	int age;		// 年龄
	int height;		// 身高
};

// 使用 全局函数 实现 运算符重载 
// 重载 + 运算符
// 实现两个 Student 对象相加
Student operator+(Student& s1, Student& s2)
{
    
    
	Student student(s1.age + s2.age, s1.height + s2.height);
	return student;
};

// 使用 全局函数 实现 前置 ++ 自增运算符重载
// 重载 前置 ++ 运算符
// 实现 1 个 Student 对象 自增运算
// 由于 参数中的 Student& s 中的属性发生了变化 
// 返回时仍需要返回 Student& s 参数本身
Student& operator++(Student& s)
{
    
    
	s.age++;
	s.height++;
	return s;
};

// 使用 全局函数 实现 前置 -- 自减运算符重载
// 重载 前置 -- 运算符
// 实现 1 个 Student 对象 自减运算
// 由于 参数中的 Student& s 中的属性发生了变化 
// 返回时仍需要返回 Student& s 参数本身
Student& operator--(Student& s)
{
    
    
	s.age--;
	s.height--;
	return s;
};

int main() {
    
    
	// 自定义类型相加
	Student s1(10, 120), s2(18, 170);
	Student s3, s4, s5;

	++s1;
	s1.print();

	--s1;
	s1.print();

    // 控制台暂停 , 按任意键继续向后执行
    system("pause");

    return 0;
};

Results of the :

age = 11 , height = 121
age = 10 , height = 120
请按任意键继续. . .