在二进制文件中使用 fread 读取时缺少值

Question

我有一个二进制文件，我在其中编写包含以下字段的结构

typedef struct super_bloque{
    size_t s_filesystem_type;
    size_t s_inodes_count;
    size_t s_blocks_count;
    size_t s_free_blocks_count;
    size_t s_free_inodes_count;
    time_t s_mtime;
    time_t s_umtime;
    size_t s_mnt_count;
    size_t s_magic;
    size_t s_inode_size;
    size_t s_block_size;
    size_t s_first_ino;
    size_t s_first_blo;
    size_t s_bm_inode_start;
    size_t s_bm_block_start;
    size_t s_inode_start;
    size_t s_block_start;    
}SUPER_BLOQUE;

我有以下方法在文件中写入结构

void Operacion::formatear_ext2(char type, size_t part_start, size_t part_size, FILE *disco){
    MBR mbr;
    fseek(disco, 0, SEEK_SET);
    fread(&mbr, sizeof(mbr), 1, disco);
    size_t n = (size_t)floor((part_size - sizeof(SUPER_BLOQUE)) / (sizeof(I_NODO) + 3 * sizeof(BLOQUE_ARCHIVO) + 4));
    printf("n = %zu\n", n);
    SUPER_BLOQUE super_block;
    memset(&super_block, 0, sizeof(SUPER_BLOQUE));
    super_block.s_filesystem_type = (size_t)2;
    super_block.s_inodes_count = n;
    super_block.s_blocks_count = (size_t)3 * n;
    super_block.s_free_blocks_count = (size_t)3 * n;
    super_block.s_free_inodes_count = n;
    super_block.s_mtime = time(0);
    super_block.s_umtime = time(0);
    super_block.s_mnt_count = 1;
    super_block.s_magic = 0xEF53;
    super_block.s_inode_size = sizeof(I_NODO);
    super_block.s_block_size = sizeof(BLOQUE_ARCHIVO);
    super_block.s_first_ino = 0;
    super_block.s_first_blo = 0;
    super_block.s_bm_inode_start = part_start + sizeof(SUPER_BLOQUE);
    super_block.s_bm_block_start = part_start + sizeof(SUPER_BLOQUE) + n;
    super_block.s_inode_start = part_start + sizeof(SUPER_BLOQUE) + n + 3 * n;
    super_block.s_block_start = part_start + sizeof(SUPER_BLOQUE) + n + 3 * n + n * sizeof(I_NODO);
    fseek(disco, part_start, SEEK_SET);
    fwrite(&super_block, sizeof(SUPER_BLOQUE), 1, disco);

    for(size_t i = 0; i < super_block.s_inodes_count; i++){
       fseek(disco, super_block.s_first_ino + i, SEEK_SET);
       fwrite("0", 1, 1, disco);
    }
    for(size_t i = 0; i < super_block.s_blocks_count; i++){ 
       fseek(disco, super_block.s_first_blo + i, SEEK_SET);
       fwrite("0", 1, 1, disco);
    }
    if(type == '1'){ 
        size_t tam_ino_bloq = super_block.s_block_start + n * sizeof(BLOQUE_ARCHIVO); 
       for(size_t i = super_block.s_inode_start; i < tam_ino_bloq; i++){
        fseek(disco, i, SEEK_SET);
        fwrite("\0", 1, 1, disco);
      }
   }

然后我读取磁盘内部的结构来检查数据是否存储正确

fseek(disco, part_start, SEEK_SET);
    fread(&tmp_sb, sizeof(SUPER_BLOQUE), 1, disco);
    printf("**************************** SUPERBLOQUE ****************************\n");
    printf("fs: %zu\n", tmp_sb.s_filesystem_type);
    printf("i-nodes count : %zu\n", tmp_sb.s_inodes_count);
    printf("blocks count : %zu\n", tmp_sb.s_blocks_count);
    printf("free blocks count: %zu\n", tmp_sb.s_free_blocks_count);
    printf("free i-nodes count: %zu\n", tmp_sb.s_free_inodes_count);
    printf("i-nodes size: %zu\n", tmp_sb.s_inode_size);
    printf("blocks size: %zu\n", tmp_sb.s_block_size);
    printf("first ino: %zu\n", tmp_sb.s_first_ino);
    printf("first blo: %zu\n", tmp_sb.s_first_blo);
    printf("bm i-node start: %zu\n", tmp_sb.s_bm_inode_start);
    printf("bm block start: %zu\n", tmp_sb.s_bm_block_start);
    printf("i-node start: %zu\n", tmp_sb.s_inode_start);
    printf("block start: %zu\n", tmp_sb.s_block_start);
    printf("***********************************************************************");
} // Finish the method

struct在写的时候有如下信息

fs: 2
i-nodes count : 64
blocks count : 192
free blocks count: 192
free i-nodes count: 64
i-nodes size: 120
blocks size: 64
first ino: 0
first blo: 0
bm i-node start: 272
bm block start: 336
i-node start: 528
block start: 8208

但是当我阅读信息时，我得到以下结果，信息已经丢失

fs: 3472328296227680304
i-nodes count : 3472328296227680304
blocks count : 3472328296227680304
free blocks count: 3472328296227680304
free i-nodes count: 3472328296227680304
i-nodes size: 120
blocks size: 64
first ino: 0
first blo: 0
bm i-node start: 272
bm block start: 336
i-node start: 528
block start: 8208

前五个字段包含垃圾。为什么会这样？感谢您的帮助

注意：我已经添加了该方法的所有行。我正在使用 Ubuntu 发行版。要打开文件，我使用以下说明

FILE *disco;
disco = fopen(path, "r+b");
if(disco){                        
  if(cmd.fs == '2'){
    formatear_ext2(cmd.type, meta->part_start, meta->part_size, disco);
  }else if(cmd.fs == '3'){
    formatear_ext3(cmd.type, meta->part_start, meta->part_size, disco);                
  }else{
    printf("ERROR\n");
  }
}else{
  printf("ERROR: No se pudo acceder al dispositivo.\n");
}

Answer 1

添加一些代码后，我仍然不知道cmd,meta,I_NODO,BLOQUE_ARCHIVO... 以及它们的值是什么。
我试图从日志中推测值以便可以编译和运行，我找到了值3472328296227680304，就像@Scheff 所说，0x3030303030303030 是由下面的代码编写的（"0" 的值是0x30）

    for(size_t i = 0; i < super_block.s_inodes_count; i++){
       fseek(disco, super_block.s_first_ino + i, SEEK_SET);
       fwrite("0", 1, 1, disco);
    }
    for(size_t i = 0; i < super_block.s_blocks_count; i++){ 
       fseek(disco, super_block.s_first_blo + i, SEEK_SET);
       fwrite("0", 1, 1, disco);
    }

如果我注释掉部分代码，奇数值不会出现
由于信息丢失，我无法准确指出错误，但我认为这会有所帮助
我建议您添加一些调试代码，例如打印出super_block.s_first_ino 值，以查找错误。