用c语言设计一个简单的二级文件系统

二级文件系统是指文件系统中有两个层次的目录结构，其中最上层的目录被称为根目录，每个目录下面可以包含多个文件或者子目录。在C语言中，可以通过文件操作函数实现简单的二级文件系统。以下是一个简单的实现示例：

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

#define MAX_FILE_SIZE 1024
#define MAX_NUM_FILES 100
#define MAX_FILENAME_LEN 20

struct file {
    char name[MAX_FILENAME_LEN];
    char data[MAX_FILE_SIZE];
    int size;
};

struct directory {
    char name[MAX_FILENAME_LEN];
    struct file files[MAX_NUM_FILES];
    int num_files;
};

struct directory root;

void init_root() {
    strcpy(root.name, "/");
    root.num_files = 0;
}

struct directory* find_directory(char* path) {
    struct directory* dir = &root;
    char* token = strtok(path, "/");
    while (token != NULL) {
        int found = 0;
        for (int i = 0; i < dir->num_files; i++) {
            if (strcmp(token, dir->files[i].name) == 0 && dir->files[i].size == -1) {
                dir = (struct directory*)dir->files[i].data;
                found = 1;
                break;
            }
        }
        if (!found) {
            return NULL;
        }
        token = strtok(NULL, "/");
    }
    return dir;
}

struct file* find_file(char* path) {
    struct directory* dir = find_directory(path);
    if (dir == NULL) {
        return NULL;
    }
    char* filename = strrchr(path, '/') + 1;
    for (int i = 0; i < dir->num_files; i++) {
        if (strcmp(filename, dir->files[i].name) == 0 && dir->files[i].size != -1) {
            return &dir->files[i];
        }
    }
    return NULL;
}

int create_directory(char* path) {
    struct directory* dir = find_directory(path);
    if (dir == NULL) {
        return -1;
    }
    char* dirname = strrchr(path, '/') + 1;
    if (strlen(dirname) > MAX_FILENAME_LEN) {
        return -1;
    }
    if (dir->num_files >= MAX_NUM_FILES) {
        return -1;
    }
    for (int i = 0; i < dir->num_files; i++) {
        if (strcmp(dirname, dir->files[i].name) == 0) {
            return -1;
        }
    }
    struct directory* new_dir = (struct directory*)malloc(sizeof(struct directory));
    strcpy(new_dir->name, dirname);
    new_dir->num_files = 0;
    dir->files[dir->num_files].size = -1;
    strcpy(dir->files[dir->num_files].name, dirname);
    dir->files[dir->num_files].data = (char*)new_dir;
    dir->num_files++;
    return 0;
}

int create_file(char* path, char* data, int size) {
    struct directory* dir = find_directory(path);
    if (dir == NULL) {
        return -1;
    }
    char* filename = strrchr(path, '/') + 1;
    if (strlen(filename) > MAX_FILENAME_LEN) {
        return -1;
    }
    if (dir->num_files >= MAX_NUM_FILES) {
        return -1;
    }
    for (int i = 0; i < dir->num_files; i++) {
        if (strcmp(filename, dir->files[i].name) == 0) {
            return -1;
        }
    }
    if (size > MAX_FILE_SIZE) {
        return -1;
    }
    strcpy(dir->files[dir->num_files].name, filename);
    memcpy(dir->files[dir->num_files].data, data, size);
    dir->files[dir->num_files].size = size;
    dir->num_files++;
    return 0;
}

int delete_file(char* path) {
    struct directory* dir = find_directory(path);
    if (dir == NULL) {
        return -1;
    }
    char* filename = strrchr(path, '/') + 1;
    for (int i = 0; i < dir->num_files; i++) {
        if (strcmp(filename, dir->files[i].name) == 0 && dir->files[i].size != -1) {
            for (int j = i; j < dir->num_files - 1; j++) {
                dir->files[j] = dir->files[j + 1];
            }
            dir->num_files--;
            return 0;
        }
    }
    return -1;
}

int main() {
    init_root();
    create_directory("/test");
    create_file("/test/file1", "hello", 5);
    create_file("/test/file2", "world", 5);
    struct file* file = find_file("/test/file1");
    if (file != NULL) {
        printf("file1 data: %s\n", file->data);
    }
    delete_file("/test/file1");
    file = find_file("/test/file1");
    if (file == NULL) {
        printf("file1 not found\n");
    }
    return 0;
}

在这个示例中，通过结构体`directory`和`file`来表示目录和文件。`root`表示根目录，`init_root()`函数用来初始化根目录。`find_directory()`函数用来查找指定路径下的目录，`find_file()`函数用来查找指定路径下的文件。`create_directory()`函数用来创建目录，`create_file()`函数用来创建文件，`delete_file()`函数用来删除文件。在主函数中，先创建了一个名为`/test`的目录，然后创建了两个文件`/test/file1`和`/test/file2`，最后查找并输出了`/test/file1`的内容，并删除了`/test/file1`。