SetFilePointerEx fails to read physical disk beyond size of LONG - winapi

Question

It's taken a few years, but I am finally taking the plunge into VC++. I need to be able to read x number of sectors of a physical device (namely a hard drive). I am using the CreateFile() and SetFilePointerEx() and ReadFile() APIs.
I have done a LOT of reading online in all the major forums about this topic. I have exhausted my research and now I feel it's time to ask the experts to weigh in on this dilemma. As this is my very first post ever on this topic, please go easy on my :)
I should also point out that this is a .DLL that I consume with a simple C# app. The plumbing all works fine. It's the SetFilePointer(Ex)() APIs that are causing me grief.
I can get the code to work up until about the size of a LONG (4,xxx,xxx) - I can't remember the exact value. It suffices to say that I can read everything up to and including sector # 4,000,000 but not 5,000,000 or above. The problem lies in the "size" of the parameters for the SetFilePointer() and SetFilePointerEx() APIs. I've tried both and so far, SetFilePointerEx() seems to be what I should use to work on 64-bit systems.
The 2nd and 3rd parameters of the SetFilePointer are defined as follows:
BOOL WINAPI SetFilePointerEx(
__in HANDLE hFile,
__in LARGE_INTEGER liDistanceToMove,
__out_opt PLARGE_INTEGER lpNewFilePointer,
__in DWORD dwMoveMethod
);
Please note that I have tried passing the LowPart and the HighPart as the 2nd and 3 parameters without any success as I get a CANNOT CONVERT LARGE_INTEGER TO PLARGE_INTEGER (for parameter 3).
HERE IS MY CODE. I USE A CODE-BREAK TO VIEW buff[0], etc. I would like to read past the 4,xxx,xxx limitation. Obviously I am doing something wrong. Each read past this limit resets my file pointer to sector 0.
#include "stdafx.h"
#include <windows.h>
#include <conio.h>
extern "C"
__declspec(dllexport) int ReadSectors(long startSector, long numSectors)
{
HANDLE hFile;
const int SECTOR_SIZE = 512;
const int BUFFER_SIZE = 512;
LARGE_INTEGER liDistanceToMove;
PLARGE_INTEGER newFilePtr = NULL; // not used in this context.
// just reading from START to END
liDistanceToMove.QuadPart = startSector * SECTOR_SIZE;
DWORD dwBytesRead, dwPos;
LPCWSTR fname = L"\\\\.\\PHYSICALDRIVE0";
char buff[BUFFER_SIZE];
// Open the PHYSICALDEVICE as a file.
hFile = CreateFile(fname,
GENERIC_READ | GENERIC_WRITE,
FILE_SHARE_READ | FILE_SHARE_WRITE,
NULL,
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL,
NULL);
// Here's the API definition
/*BOOL WINAPI SetFilePointerEx(
__in HANDLE hFile,
__in LARGE_INTEGER liDistanceToMove,
__out_opt PLARGE_INTEGER lpNewFilePointer,
__in DWORD dwMoveMethod
);*/
dwPos = SetFilePointerEx(hFile, liDistanceToMove, NULL, FILE_BEGIN);
if(ReadFile(hFile, buff, BUFFER_SIZE, &dwBytesRead, NULL))
{
if(dwBytesRead > 5)
{
BYTE x1 = buff[0];
BYTE x2 = buff[1];
BYTE x3 = buff[2];
BYTE x4 = buff[3];
BYTE x5 = buff[4];
}
}
// Close both files.
CloseHandle(hFile);
return 0;
}

Answer 1

startSector * SECTOR_SIZE;
startSector is a long (32bits), SECTOR_SIZE is a int (also 32bits), multiply these two guys and the intermediate result is going to be a long, which will overflow and you then stuff it into the __int64 of the LARGE_INTEGER, which is too late. You want to operate on __int64s, something like
liDistanceToMove.QuadPart = startSector;
liDistanceToMove.QuadPart *= SECTOR_SIZE;
for example.