Reading disk sectors directly in C/C++.

This is a discussion on Reading disk sectors directly in C/C++. within the C Programming forums, part of the General Programming Boards category; How do i directly read the disk sectors on my HDD in Turbo C/C++?I am working in win98 environment.'absread' or ...

  1. #1
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    Reading disk sectors directly in C/C++.

    How do i directly read the disk sectors on my HDD in Turbo C/C++?I am working in win98 environment.'absread' or 'abswrite' gives 'Unknown error"
    When i use F8 and get the machine into DOS,the error changes to "invalid function number".All this works fine when I change the drive to A: drive but not when i change it to C or D or E i.e HD drives.
    Is there any function in VC++ which can give direct access to the HDD ?
    Thanks in advance.

  2. #2
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    Since you're on Win98 with Turbo C, the following routine worked for me:
    Code:
    int GetSector()
    {
        int s, c, h, d;
        union
        {   char  ch[0x10];
            short sh[0x08];
            long  lg[0x04];
        } extbuf;
    
        if (Drive < 0) Drive= 0x80;
        if (Sector< 0)
        {
            printf("No Sector specified\n");
            return (-1);
        }
    
        reg.r_ax = 0x4200;
        reg.r_dx = Drive;
        reg.r_si = FP_OFF(extbuf.ch);
        reg.r_ds = FP_SEG(extbuf.ch);
    
        extbuf.ch[0] = 0x10;
        extbuf.ch[1] = 0;
        extbuf.sh[1] = 1;
        extbuf.sh[2] = FP_OFF(getbuf);
        extbuf.sh[3] = FP_SEG(getbuf);
        extbuf.lg[2] = Sector;
        extbuf.lg[3] = 0;
    
        intr(0x13, &reg);
    
        if (reg.r_flags & CF)
        {
            printf("Error %02X \n", reg.r_ax);
            return (1);
        }
        return (NO_ERROR);
    }
    Drive C: is 0x80, as defaulted above
    Variables Drive and Sector are global.
    Definition: Politics -- Latin, from
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    Question Using inbuilt function ?

    Thanks for the code.I will try to use it.But,why can't i use any inbuilt functions,after all roads leads to BIOS services !!!

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    Re: Using inbuilt function ?

    Originally posted by someonenearHim
    Thanks for the code.I will try to use it.But,why can't i use any inbuilt functions,after all roads leads to BIOS services !!!
    That is in-built. That's how Turbo accesses the interrupts and disk.

    What are you looking for? A function they wrote called
    ReadAbsoluteDiskSector(buffer,drive,sector)?

    If they had one, I might have used it. They didn't, so I had to supply it.
    Definition: Politics -- Latin, from
    poly meaning many and
    tics meaning blood sucking parasites
    -- Tom Smothers

  5. #5
    &TH of undefined behavior Fordy's Avatar
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    You can open a handle to a disk with the API CreateFile and read/write sectors from that....but from memory I dont think method this is available with Windows 98 (you need a recent NT based system)

    Also if you are looking for an API route to this, dump the Turbo C complier...it's DOS based and pretty much junkware. Go for a free, updated, windows ready compiler like MingW or Borland's Free Comandline Tools. Unless you want to spend some money on a compiler like VC++ or Codewarrior

  6. #6
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    Originally posted by Fordy
    You can open a handle to a disk with the API CreateFile and read/write sectors from that....but from memory I dont think method this is available with Windows 98 (you need a recent NT based system)
    Doesn't CreateFile ... um .. Create a File? how would you "directly read the disk sectors on my HDD" by creating a file, as someonenearHim asked? And if it's not available in 98....

  7. #7
    & the hat of GPL slaying Thantos's Avatar
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    The CreateFile function creates or opens the following objects and returns a handle that can be used to access the object:

    files
    pipes
    mailslots
    communications resources
    disk devices (Windows NT only)
    consoles
    directories (open only)
    It works on 95 and up.

    Edit: The function works on 95 and up, not sure if using that to directly access the harddrive will work on 95 or 98 though.
    Last edited by Thantos; 01-14-2004 at 06:37 PM.

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    Exclamation Where did 'file' come from ?

    Hello,
    I do not want to create or read any file directly from the HDD.I want to read the root directory of my HDD modify some values in it.I do not wish to create any handle to any file or directory.

  9. #9
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    As I posted....
    I wrote it to do exactly what you want to do.
    Definition: Politics -- Latin, from
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    tics meaning blood sucking parasites
    -- Tom Smothers

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    Thanks.

    Thanks WaltP.

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    Talking What about XP ?

    Is is possible to directly read disk sectors through TC when i am running WinXP ?

  12. #12
    &TH of undefined behavior Fordy's Avatar
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    As I said, CreateFile can open a handle to a disk on an NT system, then you can use this handle to read raw disk sectors....no files or directories involved - read the documentation at MSDN

    >>Is is possible to directly read disk sectors through TC when i am running WinXP ?

    Maybe with the old DOS interupt method mentioned above, but it's old and XP doesnt have to run that code if it doesnt want to. Again, the problem is your crappy compiler (TC) - it's a museum piece - dump it and get something half decent

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    Unhappy Couldnt get the code to work

    Hello WaltP,
    You helpfully gave me the code but i could not get it to work.The compiler says that 'reg',setbuf' is not defined.And the character placed inside the intr() function is illegal(0xae). Can you(please ofcourse) give me the main() function which could use the GetSector() function ?


    Again, the problem is your crappy compiler (TC) - it's a museum piece - dump it and get something half decent
    Can anybody suggest a better compiler for the DOS environment ?
    Last edited by someonenearHim; 01-15-2004 at 11:55 AM.

  14. #14
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    Sorry about that. I cut it from a longer file and forgot the header info. Add:
    Code:
    #include <dos.h>
    #define SECTSIZE  1024
    struct REGPACK reg;
    #define CF 1  /* carry flag */
    
    unsigned char newbuf[SECTSIZE];
    unsigned char getbuf[SECTSIZE];
    
    long Sector = -1L;
    long Drive  = -1L;
    And if you want to run it in 98, don't dump the crappy compiler. It works great for 95,98,ME. You need the crap that was removed by the latest and greatest compilers that Fordy would like you to move to.

    Is is possible to directly read disk sectors through TC when i am running WinXP ?
    No, this form won't work. The interrupts have been removed and a completely new I/O subsystem has been installed.
    Definition: Politics -- Latin, from
    poly meaning many and
    tics meaning blood sucking parasites
    -- Tom Smothers

  15. #15
    &TH of undefined behavior Fordy's Avatar
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    Originally posted by WaltP
    You need the crap that was removed by the latest and greatest compilers that Fordy would like you to move to.
    If he wants a decent free dos compiler then try http://www.delorie.com/djgpp/

    That's leaps and bounds above TurboC

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