读取FAT16文件系统

Question

我试图读取一个FAT16文件系统，以获取有关它的信息，如扇区的数目，集群，字节列表等。

我正试着这样读：

FILE *floppy;
unsigned char bootDisk[512];
floppy = fopen(name, "r");
fread(bootDisk, 1, 512, floppy);

int i;
for (i = 0; i < 80; i++){
    printf("%u,",bootDisk[i]);  
}

它的产出如下：

235,60,144,109,107,100,111,115,102,115,0,0,2,1,1,0,2,224,0,64,11,240,9,0,18,0,2,0,0,0,0,0,0,0,0,0,0,0,41,140,41,7,68,32,32,32,32,32,32,32,32,32,32,32,70,65,84,49,50,32,32,32,14,31,190,91,124,172,34,192,116,11,86,180,14,187,7,0,205,16,

这些数字代表什么?它们是什么类型的？字节？

Answer 1

您没有正确地读取这些值。它们中的大多数都大于1字节。

从等级库中可以获得引导扇区中每个属性的长度和含义：

Offset  Size (bytes)    Description
0000h   3 Code to jump to the bootstrap code.
0003h   8 Oem ID - Name of the formatting OS
000Bh   2 Bytes per Sector
000Dh   1 Sectors per Cluster - Usual there is 512 bytes per sector.
000Eh   2 Reserved sectors from the start of the volume.
0010h   1 Number of FAT copies - Usual 2 copies are used to prevent data loss.
0011h   2 Number of possible root entries - 512 entries are recommended.
0013h   2 Small number of sectors - Used when volume size is less than 32 Mb.
0015h   1 Media Descriptor
0016h   2 Sectors per FAT
0018h   2 Sectors per Track
001Ah   2 Number of Heads
001Ch   4 Hidden Sectors
0020h   4 Large number of sectors - Used when volume size is greater than 32 Mb.
0024h   1 Drive Number - Used by some bootstrap code, fx. MS-DOS.
0025h   1 Reserved - Is used by Windows NT to decide if it shall check disk integrity.
0026h   1 Extended Boot Signature - Indicates that the next three fields are available.
0027h   4 Volume Serial Number
002Bh   11 Volume Label - Should be the same as in the root directory.
0036h   8 File System Type - The string should be 'FAT16 '
003Eh   448 Bootstrap code - May schrink in the future.
01FEh   2   Boot sector signature - This is the AA55h signature

您可能应该使用自定义结构来读取引导扇区。

比如：

typedef struct {
unsigned char jmp[3];
char oem[8];
unsigned short sector_size;
unsigned char sectors_per_cluster;
unsigned short reserved_sectors;
unsigned char number_of_fats;
unsigned short root_dir_entries;
[...]
} my_boot_sector;

在你的实现中要记住你的执着和填充规则。这个结构只是一个例子。

如果您需要更多的细节，这就是一个彻底的例子。