C++ 类(class)与结构体(struct)#

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class SmartArray {
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private:
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    int* data;
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    int size;
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public:
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    // 构造函数
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    SmartArray(int sz) {
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        size = sz;
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        data = new int[size]; // 分配资源
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        std::cout << "SmartArray created.\n";
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    }
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    // 析构函数
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    ~SmartArray() {
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        delete[] data; // 释放资源
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        data = nullptr;
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        std::cout << "SmartArray destroyed.\n";
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    }
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};
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void test() {
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    SmartArray arr(10); // 在这里，构造函数被调用
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} // test函数结束，arr离开作用域，析构函数在这里被自动调用

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class Window {
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private:
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    int width, height;
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public:
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    void setDimensions(int width, int height) {
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        // 使用 this-> 来区分成员变量和同名的参数
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        this->width = width;
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        this->height = height;
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    }
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};

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#include <iostream>
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#include <string>
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#include <stdexcept> // 用于异常处理
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// --- 1. class 的定义 ---
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// 我们设计一个银行账户类
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class BankAccount {
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private: // [封装] 数据成员是私有的，保护它们不被外部随意修改
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    std::string owner_name;
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    double balance;
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public: // [接口] 成员函数是公有的，提供与对象交互的唯一途径
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    // --- 构造函数 ---
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    // 创建对象时必须提供户主名和初始余额
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    BankAccount(const std::string& owner, double initial_balance) {
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        owner_name = owner;
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        // 保证初始余额不能为负
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        if (initial_balance < 0) {
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            balance = 0;
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            std::cout << "Warning: Initial balance cannot be negative. Set to 0.\n";
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        } else {
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            balance = initial_balance;
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        }
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        std::cout << "Account for " << owner_name << " created with balance: "
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                  << balance << std::endl;
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    }
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    // --- 成员函数 (Methods) ---
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    // 存款
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    void deposit(double amount) {
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        if (amount > 0) {
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            balance += amount;
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            std::cout << "Deposited: " << amount << ". New balance: " << balance << std::endl;
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        } else {
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            std::cout << "Error: Deposit amount must be positive." << std::endl;
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        }
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    }
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    // 取款
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    void withdraw(double amount) {
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        if (amount <= 0) {
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            std::cout << "Error: Withdraw amount must be positive." << std::endl;
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            return;
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        }
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        if (amount > balance) {
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            std::cout << "Error: Insufficient funds." << std::endl;
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        } else {
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            balance -= amount;
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            std::cout << "Withdrew: " << amount << ". New balance: " << balance << std::endl;
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        }
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    }
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    // 查询余额 (const 成员函数)
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    // 'const' 关键字保证这个函数不会修改任何成员变量
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    double getBalance() const {
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        return balance;
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    }
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    // 获取户主名
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    std::string getOwnerName() const {
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        return owner_name;
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    }
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};
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// --- 2. 使用 struct 定义一个简单的数据聚合类型 ---
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struct Transaction {
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    std::string type;
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    double amount;
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};
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// --- 3. main 函数: 使用我们创建的类和结构体 ---
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int main() {
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    // 创建一个 BankAccount 对象，构造函数被自动调用
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    std::cout << "--- Creating accounts ---\n";
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    BankAccount alice_account("Alice", 500.0);
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    BankAccount bob_account("Bob", -100.0); // 测试构造函数中的验证逻辑
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    std::cout << "\n--- Performing transactions ---\n";
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    // 使用 public 接口与对象交互
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    alice_account.deposit(200.0);
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    alice_account.withdraw(150.0);
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    alice_account.withdraw(1000.0); // 测试余额不足
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    bob_account.deposit(300.0);
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    // alice_account.balance = 1000000; // ❌ 编译错误！balance是private的，不能直接访问
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    std::cout << "\n--- Final Balances ---\n";
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    std::cout << alice_account.getOwnerName() << "'s final balance is: "
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              << alice_account.getBalance() << std::endl;
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    std::cout << bob_account.getOwnerName() << "'s final balance is: "
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              << bob_account.getBalance() << std::endl;
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    // 使用 struct
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    Transaction t;
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    t.type = "DEPOSIT"; // 合法，因为struct成员默认是public
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    t.amount = 200.0;
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    std::cout << "\nTransaction recorded: " << t.type << ", Amount: " << t.amount << std::endl;
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    return 0;
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}