用C++编写一个简单的二级文件系统实现程序。要求模拟采用二级目录结构的磁盘文件系统的文件操作能实现相应的命令，用输入命令来模拟用户程序中调用的文件操作。如用一级目录创建用户、登录用户，用二级文件创建文件、删除文件和查询文件

#include <iostream>
#include <string>
#include <map>

class FileSystem {
private:
    std::map<std::string, std::map<std::string, std::string>> fileSystem;

public:
    void createUser(const std::string& username) {
        fileSystem[username] = std::map<std::string, std::string>();
        std::cout << "User '" << username << "' created." << std::endl;
    }

    void loginUser(const std::string& username) {
        if (fileSystem.find(username) != fileSystem.end()) {
            std::cout << "User '" << username << "' logged in." << std::endl;
        } else {
            std::cout << "User '" << username << "' does not exist." << std::endl;
        }
    }

    void createFile(const std::string& username, const std::string& filename) {
        if (fileSystem.find(username) != fileSystem.end()) {
            std::map<std::string, std::string>& userFiles = fileSystem[username];
            if (userFiles.find(filename) == userFiles.end()) {
                userFiles[filename] = "";
                std::cout << "File '" << filename << "' created for user '" << username << "'." << std::endl;
            } else {
                std::cout << "File '" << filename << "' already exists for user '" << username << "'." << std::endl;
            }
        } else {
            std::cout << "User '" << username << "' does not exist." << std::endl;
        }
    }

    void deleteFile(const std::string& username, const std::string& filename) {
        if (fileSystem.find(username) != fileSystem.end()) {
            std::map<std::string, std::string>& userFiles = fileSystem[username];
            if (userFiles.find(filename) != userFiles.end()) {
                userFiles.erase(filename);
                std::cout << "File '" << filename << "' deleted for user '" << username << "'." << std::endl;
            } else {
                std::cout << "File '" << filename << "' does not exist for user '" << username << "'." << std::endl;
            }
        } else {
            std::cout << "User '" << username << "' does not exist." << std::endl;
        }
    }

    void queryFile(const std::string& username, const std::string& filename) {
        if (fileSystem.find(username) != fileSystem.end()) {
            std::map<std::string, std::string>& userFiles = fileSystem[username];
            if (userFiles.find(filename) != userFiles.end()) {
                std::cout << "File '" << filename << "' found for user '" << username << "'." << std::endl;
            } else {
                std::cout << "File '" << filename << "' does not exist for user '" << username << "'." << std::endl;
            }
        } else {
            std::cout << "User '" << username << "' does not exist." << std::endl;
        }
    }
};

int main() {
    FileSystem fileSystem;

    // 创建用户
    fileSystem.createUser("user1");
    fileSystem.createUser("user2");

    // 登录用户
    fileSystem.loginUser("user1");
    fileSystem.loginUser("user3");  // 用户不存在

    // 创建文件
    fileSystem.createFile("user1", "file1");
    fileSystem.createFile("user1", "file2");
    fileSystem.createFile("user2", "file1");
    fileSystem.createFile("user2", "file3");

    // 删除文件
    fileSystem.deleteFile("user1", "file2");
    fileSystem.deleteFile("user1", "file3");  // 文件不存在

    // 查询文件
    fileSystem.queryFile("user1", "file1");
    fileSystem.queryFile("user2", "file2");  // 文件不存在

    return 0;
}