C++中的类、对象、函数、构造函数、析构函数

在C++中，类（class）是用于定义对象的模板或蓝图。类中可以包含数据成员（变量）和成员函数（方法）。对象是类的实例，通过类定义创建的实体。构造函数和析构函数是特殊的成员函数，用于对象的初始化和清理。

类和对象

定义类

类是通过class关键字定义的。类包含数据成员和成员函数。

class MyClass {
private:int data; // 数据成员public:// 成员函数void setData(int value) {data = value;}int getData() const {return data;}
};

创建对象

对象是类的实例，通过类的构造函数创建。

int main() {MyClass obj; // 创建MyClass类的对象objobj.setData(5);std::cout << "Data: " << obj.getData() << std::endl;return 0;
}

构造函数

构造函数是用于初始化对象的特殊成员函数。它们在对象创建时自动调用。构造函数的名称与类名相同，并且没有返回类型。

class MyClass {
private:int data;public:// 默认构造函数MyClass() : data(0) {std::cout << "Default constructor called" << std::endl;}// 带参数的构造函数MyClass(int value) : data(value) {std::cout << "Parameterized constructor called" << std::endl;}// 拷贝构造函数MyClass(const MyClass& other) : data(other.data) {std::cout << "Copy constructor called" << std::endl;}int getData() const {return data;}
};

析构函数

析构函数是用于清理对象的特殊成员函数。它们在对象生命周期结束时自动调用。析构函数的名称与类名相同，并且在前面加上~。析构函数也没有返回类型。

class MyClass {
private:int data;public:MyClass() : data(0) {std::cout << "Constructor called" << std::endl;}~MyClass() {std::cout << "Destructor called" << std::endl;}void setData(int value) {data = value;}int getData() const {return data;}
};

示例1

将上面几段代码连接起来，输入数据测试结果：

#include <iostream>class MyClass {
private:int data;public:// 默认构造函数MyClass() : data(0) {std::cout << "Default constructor called" << std::endl;}// 带参数的构造函数MyClass(int value) : data(value) {std::cout << "Parameterized constructor called" << std::endl;}// 拷贝构造函数MyClass(const MyClass& other) : data(other.data) {std::cout << "Copy constructor called" << std::endl;}// 析构函数~MyClass() {std::cout << "Destructor called" << std::endl;}void setData(int value) {data = value;}int getData() const {return data;}
};int main() {MyClass obj1; // 调用默认构造函数MyClass obj2(10); // 调用带参数的构造函数MyClass obj3 = obj2; // 调用拷贝构造函数obj1.setData(5);std::cout << "obj1 Data: " << obj1.getData() << std::endl;std::cout << "obj2 Data: " << obj2.getData() << std::endl;std::cout << "obj3 Data: " << obj3.getData() << std::endl;return 0;
}

输出

Default constructor called
Parameterized constructor called
Copy constructor called
obj1 Data: 5
obj2 Data: 10
obj3 Data: 10
Destructor called
Destructor called
Destructor called

示例2

实现一个用于管理银行账户的类，这个类将包含以下功能：

创建一个新账户。
存款。
取款。
查询账户余额。
. 定义银行账户类

定义一个名为BankAccount的类，它包含以下成员：

数据成员：账户余额（balance）。
成员函数：构造函数：用于初始化账户余额。存款函数：用于向账户存入金额。取款函数：用于从账户取出金额。查询余额函数：用于获取当前余额。析构函数：用于在对象销毁时输出消息。

#include <iostream>class BankAccount {
private:double balance; // 账户余额public:// 默认构造函数BankAccount() : balance(0.0) {std::cout << "Default constructor called. Account created with balance: " << balance << std::endl;}// 带参数的构造函数BankAccount(double initialBalance) : balance(initialBalance) {std::cout << "Parameterized constructor called. Account created with balance: " << balance << std::endl;}// 存款函数void deposit(double amount) {if (amount > 0) {balance += amount;std::cout << "Deposited: " << amount << ". New balance: " << balance << std::endl;} else {std::cout << "Invalid deposit amount!" << std::endl;}}// 取款函数void withdraw(double amount) {if (amount > 0 && amount <= balance) {balance -= amount;std::cout << "Withdrawn: " << amount << ". New balance: " << balance << std::endl;} else {std::cout << "Invalid withdraw amount or insufficient funds!" << std::endl;}}// 查询余额函数double getBalance() const {return balance;}// 析构函数~BankAccount() {std::cout << "Destructor called. Account with balance " << balance << " is being closed." << std::endl;}
};int main() {BankAccount account1; // 使用默认构造函数account1.deposit(100.0);account1.withdraw(30.0);std::cout << "Current balance: " << account1.getBalance() << std::endl;BankAccount account2(500.0); // 使用带参数的构造函数account2.deposit(150.0);account2.withdraw(200.0);std::cout << "Current balance: " << account2.getBalance() << std::endl;return 0;
}

输出

Default constructor called. Account created with balance: 0
Deposited: 100. New balance: 100
Withdrawn: 30. New balance: 70
Current balance: 70
Parameterized constructor called. Account created with balance: 500
Deposited: 150. New balance: 650
Withdrawn: 200. New balance: 450
Current balance: 450
Destructor called. Account with balance 70 is being closed.
Destructor called. Account with balance 450 is being closed.