Change the screen orientation in Windows programatically

ChangeScreenOrientation.c

// code copied from: http://msdn.microsoft.com/en-us/library/ms812499.aspx
// Not acutally tested on a real system

DEVMODE dm;
// initialize the DEVMODE structure
ZeroMemory(&dm, sizeof(dm));
dm.dmSize = sizeof(dm);

if (0 != EnumDisplaySettings(NULL, ENUM_CURRENT_SETTINGS, &dm))
{
  // swap height and width
  DWORD dwTemp = dm.dmPelsHeight;
  dm.dmPelsHeight= dm.dmPelsWidth;
  dm.dmPelsWidth = dwTemp;

  // determine new orientaion
  switch (dm.dmDisplayOrientation)
  {
  case DMDO_DEFAULT:
     dm.dmDisplayOrientation = DMDO_270;
     break;
  case DMDO_270:
     dm.dmDisplayOrientation = DMDO_180;
     break;
  case DMDO_180:
     dm.dmDisplayOrientation = DMDO_90;
     break;
  case DMDO_90:
     dm.dmDisplayOrientation = DMDO_DEFAULT;
     break;
  default:
     // unknown orientation value
     // add exception handling here
     break;
  }
  long lRet = ChangeDisplaySettings(&dm, 0);
  if (DISP_CHANGE_SUCCESSFUL != lRet)
  {
     // add exception handling here
  }
}