for (int i = 0; i < 26; i++)
{
    wstring s = std::wstring(L"\\.\") + wchar_t('A' + i) + L":";

    PARTITION_INFORMATION diskInfo;
    DWORD dwResult;
    HANDLE dev = CreateFile(LPWSTR(s.c_str()), GENERIC_READ, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_READONLY, NULL);
    DeviceIoControl(dev, IOCTL_DISK_GET_PARTITION_INFO, NULL, 0, &diskInfo, sizeof(diskInfo), &dwResult, NULL);
    CloseHandle(dev);
    if (diskInfo.PartitionType == PARTITION_IFS)
    {
        ...
    }
}