Why are these 2 sectors different?

Question

i tried to read ntfs partition. main function :

int main(int argc, char** argv)
{
    BYTE sector[512];
    ReadSector(L"\\\\.\\E:", 0, sector);
    PrintBPB(ReadBPB(sector));

    BYTE sector2[512];
    ReadSector(L"\\\\.\\E:", 0, sector2);
    PrintBPB(ReadBPB(sector2));
    
    return 0;
}

ReadSector function:

int ReadSector(LPCWSTR  drive, long readPoint, BYTE sector[Sector_Size])
{
    int retCode = 0;
    DWORD bytesRead;
    HANDLE device = NULL;

    device = CreateFile(drive,    // Drive to open
        GENERIC_READ,           // Access mode
        FILE_SHARE_READ | FILE_SHARE_WRITE,        // Share Mode
        NULL,                   // Security Descriptor
        OPEN_EXISTING,          // How to create
        0,                      // File attributes
        NULL);                  // Handle to template

    if (device == INVALID_HANDLE_VALUE) // Open Error
    {
        printf("CreateFile: %u\n", GetLastError());
        return 1;
    }

    SetFilePointer(device, readPoint, NULL, FILE_BEGIN);//Set a Point to Read

    if (!ReadFile(device, sector, 512, &bytesRead, NULL))
    {
        printf("ReadFile: %u\n", GetLastError());
    }
    else
    {
        printf("Success!\n");
    }
    CloseHandle(device);
}

I think the way I copy those bytes into my BPB bpb is fine.

So what happend? Why they are different? I can figure out that its relate to winapi, readfile, createfile but I still dont understand it:(

sorry for my bad english.

Answer 1

The bug is in the code we cannot see: PrintBPB . Apparently it switches to hexadecimal output (for the "Volume serial number") and then fails to switch back to decimal until later.

When the code calls PrintBPB a second time the output mode is still in hexadecimal format, and printing "Bytes per Sector" now displays 200 ( 0x200 is the same value as 512 ).

If you need to know whether two chunks of memory hold identical values, just memcmp them. This avoids introducing a bug in a transformation (such as console output).