C++中RAII资源获取即初始化

#include <memory>

void memoryManagement() {
    // 自动管理动态分配的内存
    std::unique_ptr<int> ptr(new int(42));
    
    // 无需手动delete，ptr离开作用域时自动释放内存
}

#include <fstream>

void fileOperations() {
    // 打开文件（获取资源）
    std::ifstream file("example.txt");
    
    // 读取文件内容
    // ...
    
    // 无需手动关闭文件，file离开作用域时自动关闭
}

#include <mutex>
#include <thread>

std::mutex mtx;

void lockExample() {
    // 自动加锁
    std::lock_guard<std::mutex> lock(mtx);
    
    // 临界区代码
    // ...
    
    // 无需手动解锁，lock离开作用域时自动解锁
}

#include <iostream>
#include <string>

// 模拟数据库连接资源
class DatabaseConnection {
private:
    std::string connectionString;
    bool isConnected;
    
public:
    // 构造函数：获取资源
    DatabaseConnection(const std::string& connStr) 
        : connectionString(connStr), isConnected(true) {
        std::cout << "连接到数据库: " << connectionString << std::endl;
        // 实际连接数据库的代码
    }
    
    // 析构函数：释放资源
    ~DatabaseConnection() {
        if (isConnected) {
            std::cout << "关闭数据库连接: " << connectionString << std::endl;
            // 实际关闭数据库连接的代码
            isConnected = false;
        }
    }
    
    // 禁用拷贝语义，防止资源被多次释放
    DatabaseConnection(const DatabaseConnection&) = delete;
    DatabaseConnection& operator=(const DatabaseConnection&) = delete;
    
    // 提供移动语义，允许资源转移
    DatabaseConnection(DatabaseConnection&& other) noexcept
        : connectionString(std::move(other.connectionString)),
          isConnected(other.isConnected) {
        other.isConnected = false;
    }
    
    DatabaseConnection& operator=(DatabaseConnection&& other) noexcept {
        if (this != &other) {
            // 释放当前资源
            if (isConnected) {
                std::cout << "关闭数据库连接: " << connectionString << std::endl;
                isConnected = false;
            }
            
            // 转移资源
            connectionString = std::move(other.connectionString);
            isConnected = other.isConnected;
            other.isConnected = false;
        }
        return *this;
    }
    
    // 提供资源操作接口
    void executeQuery(const std::string& query) {
        if (isConnected) {
            std::cout << "执行查询: " << query << std::endl;
            // 实际执行查询的代码
        } else {
            throw std::runtime_error("数据库连接已关闭");
        }
    }
};

void databaseExample() {
    try {
        DatabaseConnection conn("server=localhost;db=test");
        conn.executeQuery("SELECT * FROM users");
        
        // conn离开作用域时自动关闭连接
    } catch (const std::exception& e) {
        std::cerr << "错误: " << e.what() << std::endl;
    }
}

#include <iostream>
#include <memory>
#include <stdexcept>

void exceptionSafetyExample() {
    std::unique_ptr<int[]> data(new int[1000]);
    
    // 可能抛出异常的操作
    if (/* 某些条件 */) {
        throw std::runtime_error("出错了!");
    }
    
    // 即使发生异常，data也会被自动释放
}

class LazyResource {
private:
    bool initialized;
    // 资源句柄
    
public:
    LazyResource() : initialized(false) {}
    
    void useResource() {
        if (!initialized) {
            // 首次使用时获取资源
            // ...
            initialized = true;
        }
        
        // 使用资源
        // ...
    }
    
    ~LazyResource() {
        if (initialized) {
            // 释放资源
            // ...
        }
    }
};

class SharedResource {
private:
    int* data;
    int* refCount;
    
public:
    SharedResource() : data(new int(0)), refCount(new int(1)) {}
    
    SharedResource(const SharedResource& other)
        : data(other.data), refCount(other.refCount) {
        ++(*refCount);
    }
    
    SharedResource& operator=(const SharedResource& other) {
        if (this != &other) {
            release();
            data = other.data;
            refCount = other.refCount;
            ++(*refCount);
        }
        return *this;
    }
    
    ~SharedResource() {
        release();
    }
    
private:
    void release() {
        if (--(*refCount) == 0) {
            delete data;
            delete refCount;
        }
    }
};