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。

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

class File {
public:
    File(const std::string& name) : name(name) {}

    std::string getName() const {
        return name;
    }

private:
    std::string name;
};

class Directory {
public:
    Directory(const std::string& name) : name(name) {}

    std::string getName() const {
        return name;
    }

    void addFile(const std::string& fileName) {
        files[fileName] = File(fileName);
    }

    void removeFile(const std::string& fileName) {
        files.erase(fileName);
    }

    File* getFile(const std::string& fileName) {
        auto it = files.find(fileName);
        if (it != files.end()) {
            return &(it->second);
        }
        return nullptr;
    }

private:
    std::string name;
    std::map<std::string, File> files;
};

class FileSystem {
public:
    FileSystem() {
        root = new Directory("root");
    }

    ~FileSystem() {
        delete root;
    }

    void createFile(const std::string& path) {
        std::size_t pos = path.find_last_of('/');
        std::string dirPath = path.substr(0, pos);
        std::string fileName = path.substr(pos + 1);

        Directory* directory = findDirectory(dirPath);
        if (directory != nullptr) {
            directory->addFile(fileName);
        }
    }

    void deleteFile(const std::string& path) {
        std::size_t pos = path.find_last_of('/');
        std::string dirPath = path.substr(0, pos);
        std::string fileName = path.substr(pos + 1);

        Directory* directory = findDirectory(dirPath);
        if (directory != nullptr) {
            directory->removeFile(fileName);
        }
    }

    File* openFile(const std::string& path) {
        std::size_t pos = path.find_last_of('/');
        std::string dirPath = path.substr(0, pos);
        std::string fileName = path.substr(pos + 1);

        Directory* directory = findDirectory(dirPath);
        if (directory != nullptr) {
            return directory->getFile(fileName);
        }
        return nullptr;
    }

private:
    Directory* root;

    Directory* findDirectory(const std::string& path) {
        if (path == "") {
            return root;
        }

        std::size_t start = 0;
        std::size_t end = path.find_first_of('/', start);

        Directory* currDir = root;
        while (end != std::string::npos) {
            std::string dirName = path.substr(start, end - start);
            currDir = findSubDirectory(currDir, dirName);
            if (currDir == nullptr) {
                return nullptr;
            }
            start = end + 1;
            end = path.find_first_of('/', start);
        }

        std::string dirName = path.substr(start);
        return findSubDirectory(currDir, dirName);
    }

    Directory* findSubDirectory(Directory* parentDir, const std::string& dirName) {
        if (parentDir == nullptr) {
            return nullptr;
        }

        for (const auto& pair : parentDir->files) {
            if (pair.second.getName() == dirName) {
                return dynamic_cast<Directory*>(&(pair.second));
            }
        }

        return nullptr;
    }
};

int main() {
    FileSystem fileSystem;

    // 创建文件
    fileSystem.createFile("root/dir1/file1.txt");

    // 打开文件
    File* file = fileSystem.openFile("root/dir1/file1.txt");
    if (file != nullptr) {
        std::cout << "打开文件：" << file->getName() << std::endl;
    } else {
        std::cout << "文件不存在" << std::endl;
    }

    // 删除文件
    fileSystem.deleteFile("root/dir1/file1.txt");

    // 再次尝试打开文件
    file = fileSystem.openFile("root/dir1/file1.txt");
    if (file != nullptr) {
        std::cout << "打开文件：" << file->getName() << std::endl;
    } else {
        std::cout << "文件不存在" << std::endl;
    }

    return 0;
}