This is my current work-in-progress code for detecting the monitor device id, reliably.
CString DeviceID;
DISPLAY_DEVICE dd;
dd.cb = sizeof(dd);
DWORD dev = 0;
// device index
int id = 1;
// monitor number, as used by Display Properties > Settings
while (EnumDisplayDevices(0, dev, &dd, 0))
{
DISPLAY_DEVICE ddMon;
ZeroMemory(&ddMon, sizeof(ddMon));
ddMon.cb = sizeof(ddMon);
DWORD devMon = 0;
while (EnumDisplayDevices(dd.DeviceName, devMon, &ddMon, 0))
{
if (ddMon.StateFlags & DISPLAY_DEVICE_ACTIVE &&
!(ddMon.StateFlags & DISPLAY_DEVICE_MIRRORING_DRIVER))
{
DeviceID.Format (L"%s", ddMon.DeviceID);
DeviceID = DeviceID.Mid (8, DeviceID.Find (L"\\", 9) - 8);
}
devMon++;
ZeroMemory(&ddMon, sizeof(ddMon));
ddMon.cb = sizeof(ddMon);
}
ZeroMemory(&dd, sizeof(dd));
dd.cb = sizeof(dd);
dev++;
}