Why does EnumDisplayMonitors Still Return just Disconnected Monitor

Question

Why does EnumDisplayMonitors Still Return just Disconnected Monitor

Harshithraj1871 1,756

I'm working om win32 Desktop application in CPP and I'm checking what happens if I try to fetch Display info with EnumDisplayMonitors when All displays are disconnected! Surprisingly it is giving display info of previously connected Display. Why is this so? Is it returning cached info?

RLWA32 52,551 Reputation points

2025-02-11T08:33:43.86+00:00

If you use multiple monitors what does Device Manager show before disconnecting one of them and then after reconnecting it? Then try it again after scanning for hardware changes.
Harshithraj1871 1,756 Reputation points

2025-02-11T08:35:46.6166667+00:00

When we have multiple monitor the behaviours are fair, before disconnecting it will show 2 and after that it will show 1
RLWA32 52,551 Reputation points

2025-02-11T08:37:34.07+00:00

Is a manual scan for hardware changes needed to get the expected results?
Harshithraj1871 1,756 Reputation points

2025-02-11T08:40:45.1333333+00:00

Yes actually we want to do a manual scan before we bring up our window
RLWA32 52,551 Reputation points

2025-02-11T08:59:14.5166667+00:00

Maybe you could use WMI and the Win32_DesktopMonitor class to identify a disconnected monitor.
Castorix31 91,871 Reputation points

2025-02-11T09:12:33.2+00:00

Can't you use DISPLAY_DEVICE with DISPLAY_DEVICE_ACTIVE or DISPLAY_DEVICE_ATTACHED ?

Harshithraj1871 1,756

@Castorix31 tried that with EnumDisplayDevices(), I have 1 Display connected, still it gave me 4 displays (1 active and 3 inactive).

Display Device 0: \\.\DISPLAY1 - Intel(R) UHD Graphics 770
  Status: Inactive
  Primary Display: No
  Could not retrieve display settings.
---------------------------------
Display Device 1: \\.\DISPLAY2 - Intel(R) UHD Graphics 770
  Status: Active
  Primary Display: Yes
    Monitor 0: \\.\DISPLAY2\Monitor0 - Generic PnP Monitor
  Screen Resolution: 1920 x 1080 pixels
  Refresh Rate: 60 Hz
---------------------------------
Display Device 2: \\.\DISPLAY3 - Intel(R) UHD Graphics 770
  Status: Inactive
  Primary Display: No
  Could not retrieve display settings.
---------------------------------
Display Device 3: \\.\DISPLAY4 - Intel(R) UHD Graphics 770
  Status: Inactive
  Primary Display: No
  Could not retrieve display settings.
---------------------------------

And when i unplugged the my only monitor it still gave me 4 displays (1 active and 3 inactive).

Display Device 0: \\.\DISPLAY1 - Intel(R) UHD Graphics 770
  Status: Active
  Primary Display: Yes
    Monitor 0: \\.\DISPLAY1\Monitor0 - Digital Flat Panel (640x480 60Hz)
  Screen Resolution: 1920 x 1080 pixels
  Refresh Rate: 60 Hz
---------------------------------
Display Device 1: \\.\DISPLAY2 - Intel(R) UHD Graphics 770
  Status: Inactive
  Primary Display: No
  Could not retrieve display settings.
---------------------------------
Display Device 2: \\.\DISPLAY3 - Intel(R) UHD Graphics 770
  Status: Inactive
  Primary Display: No
  Could not retrieve display settings.
---------------------------------
Display Device 3: \\.\DISPLAY4 - Intel(R) UHD Graphics 770
  Status: Inactive
  Primary Display: No
  Could not retrieve display settings.
---------------------------------

EDIT : after using DISPLAY_DEVICE_ATTACHED_TO_DESKTOP flag all the inactive enumeration can be skipped but when no display is connected - i will still get an Active display as in above output

RLWA32 52,551 Reputation points

2025-02-11T16:50:13.99+00:00

Yes actually we want to do a manual scan before we bring up our window

Some posts on the internet suggested using CM_Locate_DevNode with CM_LOCATE_DEVNODE_NORMAL and CM_Reenumerate_DevNode (requires Administrator privileges) to initiate a hardware scan.
Darran Rowe 2,611 Reputation points

2025-02-11T19:40:31.53+00:00

Because that is an Intel(R) UHD Graphics adapter, is this a laptop? I'm wondering if there is something non obvious going on hardware wise, like extra hardware is being enabled when it detects an external display being plugged in.
Harshithraj1871 1,756 Reputation points

2025-02-12T06:16:25.6366667+00:00

@RLWA32 : Thanks I'm looking for some API which could run without Admin Mode
Harshithraj1871 1,756 Reputation points

2025-02-12T06:18:57.4933333+00:00

@Darran Rowe : No I'm not using Laptop. I'm using simple CPU-monitor Setup
Harshithraj1871 1,756 Reputation points

2025-02-12T09:09:17.0666667+00:00

Does windows keep any "virtual display" active even when all monitor is physically disconnected
Castorix31 91,871 Reputation points

2025-02-12T16:22:50.73+00:00

On my PC (1 monitor only), when I test both DISPLAY_DEVICE_ATTACHED && DISPLAY_DEVICE_ACTIVE, enumeration is skipped when I unplug it (Intel(R) HD Graphics and 247ELH Philips monitor)

Harshithraj1871 1,756

@Castorix31 I tried that in this way

        if (!(displayDevice.StateFlags & (DISPLAY_DEVICE_ATTACHED && DISPLAY_DEVICE_ACTIVE))) {
            deviceIndex++;
            continue;
        }
        if (!(displayDevice.StateFlags & DISPLAY_DEVICE_ATTACHED_TO_DESKTOP)) {
            deviceIndex++;
            continue;  
        }

Still I'm getting this output when no display is connected

Display Device 0: \\.\DISPLAY1 - Intel(R) UHD Graphics 770
  Status: Active
  Primary Display: Yes
    Monitor 0: \\.\DISPLAY1\Monitor0 - Digital Flat Panel (640x480 60Hz)
  Screen Resolution: 1920 x 1080 pixels
  Refresh Rate: 60 Hz
---------------------------------

Harshithraj1871 1,756 Reputation points

2025-02-19T05:46:52.0166667+00:00

.....

Harshithraj1871 1,756

@Castorix31 adding my code for better view

void GetMonitorInfoUsingDisplayDevice() {
    DISPLAY_DEVICE displayDevice;
    displayDevice.cb = sizeof(DISPLAY_DEVICE);
    int deviceIndex = 0;
    while (EnumDisplayDevices(NULL, deviceIndex, &displayDevice, 0)) {
        if (!(displayDevice.StateFlags & (DISPLAY_DEVICE_ATTACHED && DISPLAY_DEVICE_ACTIVE))) {
            deviceIndex++;
            continue;
        }
        if (!(displayDevice.StateFlags & DISPLAY_DEVICE_ATTACHED_TO_DESKTOP)) {
            deviceIndex++;
            continue;  
        }
        std::wstringstream debugMessage;
        debugMessage << L"Display Device " << deviceIndex << L": " << displayDevice.DeviceName << L" - " << displayDevice.DeviceString << L"\n";
        // Check if the display is active
        if (displayDevice.StateFlags & DISPLAY_DEVICE_ACTIVE) {
            debugMessage << L"  Status: Active\n";
        }
        else {
            debugMessage << L"  Status: Inactive\n";
        }
        // Check if it's the primary display
        if (displayDevice.StateFlags & DISPLAY_DEVICE_PRIMARY_DEVICE) {
            debugMessage << L"  Primary Display: Yes\n";
        }
        else {
            debugMessage << L"  Primary Display: No\n";
        }
        // Now, enumerate the monitor attached to this display device
        DISPLAY_DEVICE monitorDevice;
        monitorDevice.cb = sizeof(DISPLAY_DEVICE);
        int monitorIndex = 0;
        while (EnumDisplayDevices(displayDevice.DeviceName, monitorIndex, &monitorDevice, 0)) {
            debugMessage << L"    Monitor " << monitorIndex << L": " << monitorDevice.DeviceName << L" - " << monitorDevice.DeviceString << L"\n";
            monitorIndex++;
        }
        // Retrieve screen resolution using DEVMODE
        DEVMODE devMode;
        devMode.dmSize = sizeof(DEVMODE);
        if (EnumDisplaySettings(displayDevice.DeviceName, ENUM_CURRENT_SETTINGS, &devMode)) {
            debugMessage << L"  Screen Resolution: " << devMode.dmPelsWidth << L" x " << devMode.dmPelsHeight << L" pixels\n";
            debugMessage << L"  Refresh Rate: " << devMode.dmDisplayFrequency << L" Hz\n";
        }
        else {
            debugMessage << L"  Could not retrieve display settings.\n";
        }
        debugMessage << L"---------------------------------\n";
        // Send output to Visual Studio Debug window
        LogToDebugWindow(debugMessage.str());
        deviceIndex++;
    }

Anonymous

2025-02-19T06:10:16.74+00:00

Hope you've been well. Any updates about this issue?
Harshithraj1871 1,756 Reputation points

2025-02-19T06:56:05.5366667+00:00

@Anonymous I have added few comments, but this page is not showing that, looks like a bug , this happened many time.
Jeanine Zhang-MSFT 11,356 Reputation points Microsoft External Staff

2025-02-24T07:48:46.5833333+00:00

I couldn't reproduce the issue.

Could you please tell us when you connect two physical monitors and then unplug one, is the enumeration skipped?
Harshithraj1871 1,756 Reputation points

2025-02-25T05:47:53.6766667+00:00

@Jeanine Zhang-MSFT yes enumeration to the second display will be skipped. Ill only get 1 display enumeration. With the above code I shared did it skip all the display enumerations? when no display was connected?