From: ovek AT arcticnet DOT no (Ove Kåven)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: source code help
Date: Thu, 24 Oct 1996 13:57:16 GMT
Organization: Vplan Programvare AS
Lines: 39
Message-ID: <54p01c$q17@troll.powertech.no>
References: <326EBDEE DOT 4ED AT iamerica DOT net>
NNTP-Posting-Host: alwayscold.darkness.arcticnet.no
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

Jon Slaughter <lobo AT iamerica DOT net> wrote:

>here is some code that is supose to read the boot sector and print out
>all the information in BOOT_RECORD. But for some reason, it doesn't :( I
>have no idea why. It would seem that I left some variable out of the
>structure because the first two are ok, but I've looked over it and
>couldn't find anything wrong. It also could be the strings since I have
>no idea of how c handles them(except that they are null terminated)...
>Its probably something stupid, but if anyone can help me, please!!

You need to pack the structure, otherwise the fields doesn't get
aligned right, due to padding.

struct BOOT_RECORD_STRUCT {
        BYTE jump[3];
        BYTE oem_name[8];
        WORD bytes_per_sector;
        BYTE sectors_per_cluster;
        WORD number_of_reserved_sectors;
        BYTE number_of_fats;
        WORD number_of_root_dir_entries;
        WORD number_of_total_sectors;
        BYTE media_descriptor_byte;
        WORD sectors_per_fat;
        WORD sectors_per_track;
        WORD number_of_heads;
        WORD number_of_hidden_sectors1;
        WORD number_of_hidden_sectors2;
        DWORD number_of_sectors;
        BYTE physical_drive_number;
        BYTE reserved;
        BYTE signature_byte;
        DWORD volume_serial_number;
        BYTE volume_label[11];
        BYTE fat_type_char_str[8];
        BYTE filler[500];
} __attribute__((packed));        /* <=== important */