typedef BOOL (WINAPI *PFNGETDISKFREESPACEEX)(LPCTSTR, PULARGE_INTEGER, PULARGE_INTEGER, PULARGE_INTEGER);

#include <iostream>

HINSTANCE hModule = ::LoadLibrary("KERNEL32.DLL");
if(hModule)
{
  PFNGETDISKFREESPACEEX pDiskFreeSpaceEx = NULL;

  // Determine function to use
  pDiskFreeSpaceEx = reinterpret_cast<PFNGETDISKFREESPACEEX>(::GetProcAddress(hModule,
                                                                              "GetDiskFreeSpaceExA"));
  if(!pDiskFreeSpaceEx)
  {
    DWORD dwSectorsPerCluster = 0;
    DWORD dwBytesPerSector    = 0; 
    DWORD dwFreeClusters      = 0; 
    DWORD dwClusters          = 0; 

    if(::GetDiskFreeSpace(strRootPath.c_str(),
                          &dwSectorsPerCluster,
                          &dwBytesPerSector,
                          &dwFreeClusters,
                          &dwClusters) == TRUE)
      std::cout << "Available disk space = "
                << dwFreeClusters * dwBytesPerSector * dwSectorsPerCluster << " MB" << std::endl;
    else
      // Error
  }
  else
  {
    ULARGE_INTEGER uliFreeBytesAvailableToCaller;
    ULARGE_INTEGER uliTotalNumberOfBytes;
    ULARGE_INTEGER uliTotalNumberOfFreeBytes;

    if(::GetDiskFreeSpaceEx(strRootPath.c_str(),
                            &uliFreeBytesAvailableToCaller,
                            &uliTotalNumberOfBytes,
                            &uliTotalNumberOfFreeBytes) == TRUE)
      std::cout << "Available disk space = "
                << static_cast<int>(static_cast<__int64>(uliFreeBytesAvailableToCaller.QuadPart /
                                                         (1024 * 1024)))
                << " MB" << std::endl;
    else
      // Error
  }

  // Release library
  ::FreeLibrary(hModule);
}
else
  // Error -> call ::GetLastError()