Incorrect Function Call "IOCTL_DISK_GET_DRIVE_LAYOUT_EX" - c++

Question

I am currently trying to write a C++ program to automate retrieving information about the partitions of a sample hard-drive image, the information in question being the number of partitions on the disk and for each partition its start sector, size and and file system type.
I'm pretty sure at this point the best way to achieve this is through MSDN functions, microsofts inbuilt commands. I am trying to use the "IOCTL_DISK_GET_DRIVE_LAYOUT_EX" function, but according to my get error call my function is incorrect. When I debug the program is appears that the bool value is also unchanged after the "IOCTL_DISK_GET_DRIVE_LAYOUT_EX" call, meaning it is not returning the bResult value.
I am using Microsoft Visual C++ Express Edition. If people could take a look at my code and tell me what they think I did wrong it would be much appreciated.
#define UNICODE 1
#define _UNICODE 1
#include <windows.h>
#include <winioctl.h>
#include <stdio.h>
#define wszDrive L"\\\\.\\PhysicalDrive6"
BOOL GetDriveParition(LPWSTR wszPath, DRIVE_LAYOUT_INFORMATION_EX *pdg)
{
HANDLE hDevice = INVALID_HANDLE_VALUE; // handle to the drive to be examined
BOOL bResult = FALSE; // results flag
DWORD junk = 0; // discard results
hDevice = CreateFileW(wszPath, // drive to open
0, // no access to the drive
FILE_SHARE_READ | // share mode
FILE_SHARE_WRITE,
NULL, // default security attributes
OPEN_EXISTING, // disposition
0, // file attributes
NULL); // do not copy file attributes
if (hDevice == INVALID_HANDLE_VALUE) // cannot open the drive
{
return (FALSE);
}
bResult = DeviceIoControl(
hDevice, // handle to device
IOCTL_DISK_GET_DRIVE_LAYOUT_EX, // dwIoControlCode
NULL, // lpInBuffer
0, // nInBufferSize
pdg, // lpOutBuffer
sizeof(*pdg), // nOutBufferSize
&junk, // lpBytesReturned
NULL); // lpOverlapped
CloseHandle(hDevice);
return (bResult);
}
int wmain(int argc, wchar_t *argv[])
{
DRIVE_LAYOUT_INFORMATION_EX pdg; // disk drive partition structure
BOOL bResult = FALSE; // generic results flag
bResult = GetDriveParition (wszDrive, &pdg);
if (bResult)
{
wprintf(L"Drive path = %ws\n", wszDrive);
wprintf(L"Partition Style = %I64d\n", pdg.PartitionStyle);
wprintf(L"Partition Count = %ld\n", pdg.PartitionCount);
system("Pause");
}
else
{
wprintf (L"GetDrivePartition failed. Error %ld.\n", GetLastError ());
system("Pause");
}
return ((int)bResult);
}

Answer 1

DRIVE_LAYOUT_INFORMATION_EX is a weird structure. It's defined as
struct {
DWORD PartitionStyle;
DWORD PartitionCount;
union {
DRIVE_LAYOUT_INFORMATION_MBR Mbr;
DRIVE_LAYOUT_INFORMATION_GPT Gpt;
};
PARTITION_INFORMATION_EX PartitionEntry[ 1 ];
}
but usually PartitionEntry is treated as a much larger array, with PartitionCount entries. This is similar to the C99 VLA mechanism. Since you'va allocated just sizeof(*pdg) bytes, there's no room for even a second PartitionEntry.
C++ hack:
struct ExtraEntries : DRIVE_LAYOUT_INFORMATION_EX
{
PARTITION_INFORMATION_EX PartitionEntry[ 9 ]; // Or some other reasonable value
};

Answer 2

Even if this post is a bit old, I found another way to get a fully populated PartitionEntry without creating a tricky struct. This is how I did it:
Inspired of an answer from this post: How-to-call-deviceiocontrol-to-retrieve-the-amount-of-memory-it-needs
DRIVE_LAYOUT_INFORMATION_EX dli;
DWORD bytesReturned = 0;
if (!DeviceIoControl(hDevice, IOCTL_DISK_GET_DRIVE_LAYOUT_EX, NULL, 0, (void*)&dli, sizeof(dli), &bytesReturned, NULL))
{
// Check last error if not ERROR_INSUFFICIENT_BUFFER then return
int nError = GetLastError();
if (nError != ERROR_INSUFFICIENT_BUFFER)
{
// std::cout << "DeviceIoControl() Failed: " << nError << std::endl;
CloseHandle(hDevice);
return false;
}
// Allocate enough buffer space based of the value of Partition Count:
size_t size = offsetof(DRIVE_LAYOUT_INFORMATION_EX, PartitionEntry[dli.PartitionCount]);
std::vector<BYTE> buffer(size);
if (!DeviceIoControl(hDevice, IOCTL_DISK_GET_DRIVE_LAYOUT_EX, NULL, 0, (void*)buffer.data(), size, &bytesReturned, NULL))
{
nError = GetLastError();
// std::cout << "DeviceIoControl() Failed: " << nError << std::endl;
CloseHandle(hDevice);
return false;
}
const DRIVE_LAYOUT_INFORMATION_EX& result = *reinterpret_cast<const DRIVE_LAYOUT_INFORMATION_EX*>(buffer.data());
// Here all parition entry are populated ...
// TO DO... Do your stuff with result
}
else
{
// Call succeeded; dli is populated with a signle partition entry
// TO DO... Do your stuff with dli
}