How to read number of FATs from FAT filesystem?

Asked Apr 17 '21 at 18:15

Active Apr 17 '21 at 18:15

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I'm trying to read the number of FATs my FAT filesystem might have. In order to do that I'm reading as reference the documentation found here.

It's said that the number of FATs is given in the 16th byte of the binary file. But it has a length of 1 byte. From my knowledge, I know integers are at least 4 bytes long.

How can I read the number of FATs in my binary file?

I have tried reading it anyways without success:

void test(int file_descriptor) {
    int nFats;

    lseek(file_descriptor, 16, SEEK_SET);
    read(file_descriptor, &nFats, 1);

    printf("Number of FATs: %d\n", nFats);
}

asked Apr 17 '21 at 18:15

Javi Albors

1

Well a single unsigned byte will give you a number from 0 to 255. I guess it's enough for the number of FATs. Use `uint8_t`. – Tarik Apr 17 '21 at 18:18
Hint: `unsigned char` is an integer type. – Carl Norum Apr 17 '21 at 18:19
Have a look at `stdint.h` – Emanuel P Apr 17 '21 at 18:20
1

You might like to define a (packed) structure of the boot sector to access such information.It will help you also in any other work with the filesystem. – the busybee Apr 17 '21 at 19:39

How to read number of FATs from FAT filesystem?

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