用C语言写一个简单的文件系统，代码要求：具备基本的文件处理功能，包括实现文件的建立、打开、删除、关闭、复制、读、写、查询等功能，附带菜单栏。

这是一个比较复杂的项目，需要涉及到文件操作、数据结构等多方面的知识。以下是一个简单的示例代码，只实现了部分功能，仅供参考。

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

#define MAX_FILENAME_LEN 20
#define MAX_FILE_NUM 10
#define BLOCK_SIZE 1024
#define BLOCK_NUM 100
#define MAX_DATA_LEN (BLOCK_SIZE - sizeof(int))

struct file {
    char name[MAX_FILENAME_LEN];
    int size;
    int block_num;
    int block_index[BLOCK_NUM];
};

struct block {
    int next;
    char data[MAX_DATA_LEN];
};

struct file_system {
    struct file files[MAX_FILE_NUM];
    int file_num;
    struct block blocks[BLOCK_NUM];
    int free_block;
};

struct file_system fs;

void init_file_system() {
    memset(&fs, 0, sizeof(fs));
    fs.free_block = 0;
    for (int i = 0; i < BLOCK_NUM; i++) {
        fs.blocks[i].next = i + 1;
    }
    fs.blocks[BLOCK_NUM - 1].next = -1;
}

int find_file(char *name) {
    for (int i = 0; i < fs.file_num; i++) {
        if (strcmp(fs.files[i].name, name) == 0) {
            return i;
        }
    }
    return -1;
}

int find_free_block() {
    if (fs.free_block == -1) {
        return -1;
    }
    int block_index = fs.free_block;
    fs.free_block = fs.blocks[block_index].next;
    return block_index;
}

void free_block(int block_index) {
    fs.blocks[block_index].next = fs.free_block;
    fs.free_block = block_index;
}

int create_file(char *name) {
    if (find_file(name) != -1) {
        printf("File %s already exists\n", name);
        return -1;
    }
    if (fs.file_num == MAX_FILE_NUM) {
        printf("File system is full\n");
        return -1;
    }
    struct file *file = &fs.files[fs.file_num++];
    strcpy(file->name, name);
    file->size = 0;
    file->block_num = 0;
    return fs.file_num - 1;
}

int delete_file(char *name) {
    int file_index = find_file(name);
    if (file_index == -1) {
        printf("File %s not found\n", name);
        return -1;
    }
    struct file *file = &fs.files[file_index];
    for (int i = 0; i < file->block_num; i++) {
        free_block(file->block_index[i]);
    }
    memmove(&fs.files[file_index], &fs.files[file_index + 1], (fs.file_num - file_index - 1) * sizeof(struct file));
    fs.file_num--;
    return 0;
}

int open_file(char *name) {
    int file_index = find_file(name);
    if (file_index == -1) {
        printf("File %s not found\n", name);
        return -1;
    }
    return file_index;
}

int close_file(int file_index) {
    return 0;
}

int copy_file(char *src_name, char *dst_name) {
    int src_index = find_file(src_name);
    if (src_index == -1) {
        printf("File %s not found\n", src_name);
        return -1;
    }
    if (find_file(dst_name) != -1) {
        printf("File %s already exists\n", dst_name);
        return -1;
    }
    if (fs.file_num == MAX_FILE_NUM) {
        printf("File system is full\n");
        return -1;
    }
    struct file *src_file = &fs.files[src_index];
    struct file *dst_file = &fs.files[fs.file_num++];
    strcpy(dst_file->name, dst_name);
    dst_file->size = src_file->size;
    dst_file->block_num = src_file->block_num;
    for (int i = 0; i < src_file->block_num; i++) {
        int block_index = find_free_block();
        if (block_index == -1) {
            printf("File system is full\n");
            return -1;
        }
        memcpy(&fs.blocks[block_index], &fs.blocks[src_file->block_index[i]], sizeof(struct block));
        dst_file->block_index[i] = block_index;
    }
    return fs.file_num - 1;
}

int read_file(int file_index, char *buf, int len, int offset) {
    struct file *file = &fs.files[file_index];
    if (offset < 0 || offset >= file->size) {
        printf("Invalid offset %d\n", offset);
        return -1;
    }
    int read_len = len;
    if (offset + len > file->size) {
        read_len = file->size - offset;
    }
    int read_pos = 0;
    int block_offset = offset % BLOCK_SIZE;
    int block_index = file->block_index[offset / BLOCK_SIZE];
    while (read_pos < read_len) {
        int block_len = BLOCK_SIZE - block_offset;
        if (block_offset + block_len > read_len - read_pos) {
            block_len = read_len - read_pos - block_offset;
        }
        memcpy(buf + read_pos, fs.blocks[block_index].data + block_offset, block_len);
        read_pos += block_len;
        block_offset = 0;
        block_index = fs.blocks[block_index].next;
    }
    return read_len;
}

int write_file(int file_index, char *buf, int len, int offset) {
    struct file *file = &fs.files[file_index];
    if (offset < 0 || offset > file->size) {
        printf("Invalid offset %d\n", offset);
        return -1;
    }
    int write_len = len;
    if (offset + len > MAX_DATA_LEN * file->block_num) {
        printf("File is too large\n");
        return -1;
    }
    if (offset + len > file->size) {
        file->size = offset + len;
    }
    int write_pos = 0;
    int block_offset = offset % BLOCK_SIZE;
    int block_index = file->block_index[offset / BLOCK_SIZE];
    while (write_pos < write_len) {
        int block_len = BLOCK_SIZE - block_offset;
        if (block_offset + block_len > write_len - write_pos) {
            block_len = write_len - write_pos - block_offset;
        }
        memcpy(fs.blocks[block_index].data + block_offset, buf + write_pos, block_len);
        write_pos += block_len;
        block_offset = 0;
        if (write_pos < write_len) {
            int next_block_index = find_free_block();
            if (next_block_index == -1) {
                printf("File system is full\n");
                return -1;
            }
            fs.blocks[block_index].next = next_block_index;
            block_index = next_block_index;
            file->block_num++;
        }
    }
    return write_len;
}

void list_files() {
    printf("Name\tSize\n");
    for (int i = 0; i < fs.file_num; i++) {
        printf("%s\t%d\n", fs.files[i].name, fs.files[i].size);
    }
}

void print_menu() {
    printf("1. Create file\n");
    printf("2. Delete file\n");
    printf("3. Open file\n");
    printf("4. Close file\n");
    printf("5. Copy file\n");
    printf("6. Read file\n");
    printf("7. Write file\n");
    printf("8. List files\n");
    printf("9. Exit\n");
}

int main() {
    init_file_system();
    char buf[BLOCK_SIZE];
    int file_index = -1;
    while (1) {
        print_menu();
        int choice;
        printf("Enter your choice: ");
        scanf("%d", &choice);
        switch (choice) {
        case 1:
            printf("Enter file name: ");
            scanf("%s", buf);
            create_file(buf);
            break;
        case 2:
            printf("Enter file name: ");
            scanf("%s", buf);
            delete_file(buf);
            break;
        case 3:
            printf("Enter file name: ");
            scanf("%s", buf);
            file_index = open_file(buf);
            if (file_index == -1) {
                break;
            }
            printf("File %s opened\n", buf);
            break;
        case 4:
            close_file(file_index);
            file_index = -1;
            printf("File closed\n");
            break;
        case 5:
            printf("Enter source file name: ");
            scanf("%s", buf);
            printf("Enter destination file name: ");
            scanf("%s", buf + MAX_FILENAME_LEN);
            copy_file(buf, buf + MAX_FILENAME_LEN);
            break;
        case 6:
            printf("Enter offset and length: ");
            int offset, len;
            scanf("%d%d", &offset, &len);
            if (file_index == -1) {
                printf("No file opened\n");
                break;
            }
            read_file(file_index, buf, len, offset);
            printf("Data read: %.*s\n", len, buf);
            break;
        case 7:
            printf("Enter offset and data: ");
            scanf("%d%s", &offset, buf);
            if (file_index == -1) {
                printf("No file opened\n");
                break;
            }
            write_file(file_index, buf, strlen(buf), offset);
            printf("Data written\n");
            break;
        case 8:
            list_files();
            break;
        case 9:
            exit(0);
            break;
        default:
            printf("Invalid choice\n");
            break;
        }
    }
    return 0;
}