Find starting offset of a partition - c++

Question

Suppose I have a usb drive with two partition e:, f:. How do I know from which offset the partition e: or f: starts so that I can write raw data starting from that offset. I could not find any function that would provide me the offset in c++. In Dos I could easily get this with wmic partition get Index, Name, StartingOffset.

Answer 1

To get the StartingOffset of partitions in a Physical Drive(such as \\\\.\\PhysicalDrive1), you could use IOCTL_DISK_GET_DRIVE_LAYOUT_EX to get PARTITION_INFORMATION_EX arrays for each partition:
#include <windows.h>
#include <stdio.h>
#define wszDrive L"\\\\.\\PhysicalDrive1"
int wmain(int argc, wchar_t* argv[])
{
HANDLE hDevice = INVALID_HANDLE_VALUE; // handle to the drive to be examined
BOOL bResult = FALSE; // results flag
DWORD junk = 0; // discard results
DWORD error;
DWORD szNewLayout = sizeof(DRIVE_LAYOUT_INFORMATION_EX) + sizeof(PARTITION_INFORMATION_EX) * 4 * 25;
hDevice = CreateFileW(wszDrive, // drive to open
GENERIC_READ, // no access to the drive
FILE_SHARE_READ,
NULL, // default security attributes
OPEN_EXISTING, // disposition
0, // file attributes
0); // do not copy file attributes
if (hDevice == INVALID_HANDLE_VALUE) // cannot open the drive
{
error = GetLastError();
printf("CreateFileW error: %d\n", error);
return -1;
}
DRIVE_LAYOUT_INFORMATION_EX* pdg = (DRIVE_LAYOUT_INFORMATION_EX*)malloc(szNewLayout);
if (pdg == NULL)
{
error = GetLastError();
printf("malloc error: %d\n", error);
CloseHandle(hDevice);
return -1;
}
ZeroMemory(pdg, szNewLayout);
bResult = DeviceIoControl(hDevice, // device to be queried
IOCTL_DISK_GET_DRIVE_LAYOUT_EX, // operation to perform
NULL, 0, // no input buffer
pdg, szNewLayout,// sizeof(*pdg)*2, // output buffer
&junk, // # bytes returned
(LPOVERLAPPED)NULL); // synchronous I/O
if (!bResult)
{
error = GetLastError();
printf("DeviceIoControl error: %d\n", error);
free(pdg);
CloseHandle(hDevice);
return -1;
}
for (int i = 0; i < pdg->PartitionCount; i++) {
printf("partition %d: %lld\n", i, pdg->PartitionEntry[i].StartingOffset.QuadPart);
}
free(pdg);
CloseHandle(hDevice);
return 0;
}
To get the StartingOffset of a specified partition(such as \\\\.\\E:), you could use IOCTL_DISK_GET_PARTITION_INFO_EX:
#include <windows.h>
#include <stdio.h>
#define wszDrive L"\\\\.\\E:"
int wmain(int argc, wchar_t* argv[])
{
HANDLE hDevice = INVALID_HANDLE_VALUE; // handle to the drive to be examined
BOOL bResult = FALSE; // results flag
DWORD junk = 0; // discard results
DWORD error;
PARTITION_INFORMATION_EX piex;
ZeroMemory(&piex, sizeof(PARTITION_INFORMATION_EX));
hDevice = CreateFileW(wszDrive, // drive to open
GENERIC_READ, // no access to the drive
FILE_SHARE_READ,
NULL, // default security attributes
OPEN_EXISTING, // disposition
0, // file attributes
0); // do not copy file attributes
if (hDevice == INVALID_HANDLE_VALUE) // cannot open the drive
{
error = GetLastError();
printf("CreateFileW error: %d\n", error);
return -1;
}
bResult = DeviceIoControl(hDevice,
IOCTL_DISK_GET_PARTITION_INFO_EX,
NULL, 0,
&piex, sizeof(PARTITION_INFORMATION_EX),
&junk,
(LPOVERLAPPED)NULL);
if (!bResult)
{
error = GetLastError();
printf("DeviceIoControl error: %d\n", error);
CloseHandle(hDevice);
return -1;
}
wprintf(L"%s StartingOffset: %lld\n", wszDrive, piex.StartingOffset.QuadPart);
CloseHandle(hDevice);
return 0;
}