C++ application to detach secondary monitor

Question

I am trying to create an application to detach a secondary monitor from Windows boxes (long story).

Here is Microsoft's sample code that I used as a basis: http://support.microsoft.com/kb/308216/en-us

Here is my code:

#include <iostream>
#include <windows.h>

void DetachDisplay()
{
    BOOL            FoundSecondaryDisp = FALSE;
    DWORD           DispNum = 0;
    DISPLAY_DEVICE  DisplayDevice;
    LONG            Result;
    TCHAR           szTemp[200];
    int             i = 0;
    DEVMODE   defaultMode;

    // initialize DisplayDevice
    ZeroMemory(&DisplayDevice, sizeof(DisplayDevice));
    DisplayDevice.cb = sizeof(DisplayDevice);

    // get all display devices
    while (EnumDisplayDevices(NULL, DispNum, &DisplayDevice, 0))
        {
        ZeroMemory(&defaultMode, sizeof(DEVMODE));
        defaultMode.dmSize = sizeof(DEVMODE);
        if ( !EnumDisplaySettings((LPSTR)DisplayDevice.DeviceName, ENUM_REGISTRY_SETTINGS, &defaultMode) )
                  OutputDebugString("Store default failed\n");

        if ((DisplayDevice.StateFlags & DISPLAY_DEVICE_ATTACHED_TO_DESKTOP) &&
            !(DisplayDevice.StateFlags & DISPLAY_DEVICE_PRIMARY_DEVICE))
            {
            DEVMODE    DevMode;
            ZeroMemory(&DevMode, sizeof(DevMode));
            DevMode.dmSize = sizeof(DevMode);
            DevMode.dmFields = DM_PELSWIDTH | DM_PELSHEIGHT | DM_BITSPERPEL | DM_POSITION
                        | DM_DISPLAYFREQUENCY | DM_DISPLAYFLAGS ;
            Result = ChangeDisplaySettingsEx((LPSTR)DisplayDevice.DeviceName, &DevMode, NULL, CDS_UPDATEREGISTRY, NULL);
            //Result = ChangeDisplaySettingsEx((LPSTR)DisplayDevice.DeviceName, &DevMode, NULL, CDS_UPDATEREGISTRY, NULL);
            ChangeDisplaySettingsEx (NULL, NULL, NULL, 0, NULL);


            //The code below shows how to re-attach the secondary displays to the desktop

            //ChangeDisplaySettingsEx((LPSTR)DisplayDevice.DeviceName, &defaultMode, NULL, CDS_UPDATEREGISTRY, NULL);
            //ChangeDisplaySettingsEx((LPSTR)DisplayDevice.DeviceName, &defaultMode, NULL, CDS_UPDATEREGISTRY, NULL);

            }

        // Reinit DisplayDevice just to be extra clean

        ZeroMemory(&DisplayDevice, sizeof(DisplayDevice));
        DisplayDevice.cb = sizeof(DisplayDevice);
        DispNum++;
        } // end while for all display devices
}

int main()
{
    DetachDisplay();
    return 0;
}

However, when I compile and run it all I get is the screen to flicker as if it is changing resolutions but it doesn't actually do anything meaningful (I do notice the mouse moved...but other than that nothing).

Perhaps someone else has already created a utility to do this exact functionality, which would work just as good if it can be invoked from the command line.

Thoughts?

Answer 1

The code snippet above actually detaches secondary display device, not monitor. The same display device may contain multiple monitors. I haven't succeeded with this problem yet