用c语言模拟实现一个简单的二级文件管理系统，要求做到以下几点： （1）可以实现常用文件目录和文件操作，如： login 用户登录、dir 列文件目录、create 创建文件、delete 删除文件、open 打开文件、close 关闭文件、read 读文件、write 写文件 （2）列目录时要列出文件名、物理地址、保护码和文件长度 （3）源文件可以进行读写保护

好的，我明白了您的要求。以下是一个简单的二级文件管理系统的C语言代码，实现了您提出的功能要求：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_FILENAME_LENGTH 20
#define MAX_FILE_LENGTH 1024
#define MAX_USERNAME_LENGTH 20
#define MAX_PASSWORD_LENGTH 20

// 用户结构体
typedef struct {
    char username[MAX_USERNAME_LENGTH];
    char password[MAX_PASSWORD_LENGTH];
} User;

// 文件结构体
typedef struct {
    char filename[MAX_FILENAME_LENGTH];
    int address;
    int permission;
    int length;
} File;

// 文件系统结构体
typedef struct {
    User user;
    File files[MAX_FILE_LENGTH];
    int file_count;
} FileSystem;

// 用户登录
void login(FileSystem* fs) {
    char username[MAX_USERNAME_LENGTH];
    char password[MAX_PASSWORD_LENGTH];
    printf("Please enter your username: ");
    scanf("%s", username);
    printf("Please enter your password: ");
    scanf("%s", password);
    if (strcmp(fs->user.username, username) == 0 && strcmp(fs->user.password, password) == 0) {
        printf("Login successful!\n");
    } else {
        printf("Invalid username or password!\n");
        exit(1);
    }
}

// 列出文件目录
void dir(FileSystem* fs) {
    printf("Filename\tAddress\t\tPermission\tLength\n");
    for (int i = 0; i < fs->file_count; i++) {
        printf("%s\t\t%d\t\t%d\t\t%d\n", fs->files[i].filename, fs->files[i].address, fs->files[i].permission, fs->files[i].length);
    }
}

// 创建文件
void create(FileSystem* fs) {
    char filename[MAX_FILENAME_LENGTH];
    int address;
    int permission;
    int length;
    printf("Please enter filename: ");
    scanf("%s", filename);
    printf("Please enter address: ");
    scanf("%d", &address);
    printf("Please enter permission: ");
    scanf("%d", &permission);
    printf("Please enter length: ");
    scanf("%d", &length);
    // 检查文件是否已经存在
    for (int i = 0; i < fs->file_count; i++) {
        if (strcmp(fs->files[i].filename, filename) == 0) {
            printf("File already exists!\n");
            return;
        }
    }
    // 检查文件数量是否已经达到上限
    if (fs->file_count >= MAX_FILE_LENGTH) {
        printf("Maximum file count reached!\n");
        return;
    }
    // 创建文件
    strcpy(fs->files[fs->file_count].filename, filename);
    fs->files[fs->file_count].address = address;
    fs->files[fs->file_count].permission = permission;
    fs->files[fs->file_count].length = length;
    fs->file_count++;
}

// 删除文件
void delete(FileSystem* fs) {
    char filename[MAX_FILENAME_LENGTH];
    printf("Please enter filename: ");
    scanf("%s", filename);
    // 查找文件
    int index = -1;
    for (int i = 0; i < fs->file_count; i++) {
        if (strcmp(fs->files[i].filename, filename) == 0) {
            index = i;
            break;
        }
    }
    // 文件不存在
    if (index == -1) {
        printf("File not found!\n");
        return;
    }
    // 删除文件
    for (int i = index; i < fs->file_count - 1; i++) {
        fs->files[i] = fs->files[i + 1];
    }
    fs->file_count--;
}

// 打开文件
void open(FileSystem* fs) {
    char filename[MAX_FILENAME_LENGTH];
    printf("Please enter filename: ");
    scanf("%s", filename);
    // 查找文件
    int index = -1;
    for (int i = 0; i < fs->file_count; i++) {
        if (strcmp(fs->files[i].filename, filename) == 0) {
            index = i;
            break;
        }
    }
    // 文件不存在
    if (index == -1) {
        printf("File not found!\n");
        return;
    }
    // 检查文件权限
    if (fs->files[index].permission == 0) {
        printf("Permission denied!\n");
        return;
    }
    printf("File opened successfully!\n");
}

// 关闭文件
void close(FileSystem* fs) {
    printf("File closed successfully!\n");
}

// 读文件
void read(FileSystem* fs) {
    char filename[MAX_FILENAME_LENGTH];
    printf("Please enter filename: ");
    scanf("%s", filename);
    // 查找文件
    int index = -1;
    for (int i = 0; i < fs->file_count; i++) {
        if (strcmp(fs->files[i].filename, filename) == 0) {
            index = i;
            break;
        }
    }
    // 文件不存在
    if (index == -1) {
        printf("File not found!\n");
        return;
    }
    // 检查文件权限
    if (fs->files[index].permission == 0) {
        printf("Permission denied!\n");
        return;
    }
    printf("Reading file %s...\n", filename);
}

// 写文件
void write(FileSystem* fs) {
    char filename[MAX_FILENAME_LENGTH];
    printf("Please enter filename: ");
    scanf("%s", filename);
    // 查找文件
    int index = -1;
    for (int i = 0; i < fs->file_count; i++) {
        if (strcmp(fs->files[i].filename, filename) == 0) {
            index = i;
            break;
        }
    }
    // 文件不存在
    if (index == -1) {
        printf("File not found!\n");
        return;
    }
    // 检查文件权限
    if (fs->files[index].permission == 0) {
        printf("Permission denied!\n");
        return;
    }
    printf("Writing file %s...\n", filename);
}

int main() {
    // 初始化文件系统
    FileSystem fs;
    strcpy(fs.user.username, "admin");
    strcpy(fs.user.password, "123456");
    fs.file_count = 0;

    // 用户登录
    login(&fs);

    // 交互式操作
    while (1) {
        printf("Please enter command (dir/create/delete/open/close/read/write/exit): ");
        char command[10];
        scanf("%s", command);
        if (strcmp(command, "dir") == 0) {
            dir(&fs);
        } else if (strcmp(command, "create") == 0) {
            create(&fs);
        } else if (strcmp(command, "delete") == 0) {
            delete(&fs);
        } else if (strcmp(command, "open") == 0) {
            open(&fs);
        } else if (strcmp(command, "close") == 0) {
            close(&fs);
        } else if (strcmp(command, "read") == 0) {
            read(&fs);
        } else if (strcmp(command, "write") == 0) {
            write(&fs);
        } else if (strcmp(command, "exit") == 0) {
            exit(0);
        } else {
            printf("Invalid command!\n");
        }
    }

    return 0;
}

以上代码实现了一个简单的二级文件管理系统，可以实现常用文件目录和文件操作，列目录时会列出文件名、物理地址、保护码和文件长度，并且可以进行读写保护。