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Obtain Device Information Set for Monitors: Returned Handle is always INVALID_HANDLE_VALUE

2 posts in this topic



I am attempting to list the device information for all the monitors currently connected to the computer. I have a function that can do this and its 90% done except when I go to call the function SetupDiGetClassDevs() with the 2nd parameter set(not NULL) then the function always fails(returns INVALID_HANDLE_VALUE).


When I call GetLastError() I get the error 13(decimal), ie, "The data is invalid" which I am not sure what that means?

What is going wrong? Can you provide any advice on whats happening and how I can fix it?

Function Information:

HDEVINFO SetupDiGetClassDevs(
      _In_opt_  const GUID *ClassGuid,
      _In_opt_  PCTSTR Enumerator,     // According to MSDN this param MUST be set if I want Device Information for a specific class(Monitors)
      _In_opt_  HWND hwndParent,
      _In_      DWORD Flags


My function that attempts to get a Device Information Set for Monitors only and output each monitors details(the error line is commented):

void printDeviceData(GUID guID)
        // Device Classes:        http://msdn.microsoft.com/en-us/library/windows/hardware/ff553426
        // System Device Classes: http://msdn.microsoft.com/en-us/library/windows/hardware/ff553428
        // Monitor Class GUI:     {4d36e96e-e325-11ce-bfc1-08002be10318}
        DWORD dataT                    = 0;
        PCTSTR monitorGuID             = _T("");
        SP_DEVINFO_DATA deviceInfoData = {0};
        deviceInfoData.cbSize          = sizeof(SP_DEVINFO_DATA);
        deviceInfoData.ClassGuid       = guID;
        // Step 1: Get Device Information Set for Monitors only
        // ERROR OCCURS HERE: SetupDiGetClassDevs() always fails
        // Also tried these values for param 2: "Monitor" "PCI" but all cause the function to return INVALID_HANDLE_VALUE
        HDEVINFO hDevInfo = SetupDiGetClassDevs(&guID, _T("{4d36e96e-e325-11ce-bfc1-08002be10318}"), NULL, DIGCF_PRESENT | DIGCF_DEVICEINTERFACE);
        if (hDevInfo == INVALID_HANDLE_VALUE) {
            //outputLastError(_T("Fail 1"));
            printf("hDevInfo == INVALID_HANDLE_VALUE\n");
        else printf("SUCCESS 1\n");
        if (SetupDiGetSelectedDevice(hDevInfo, &deviceInfoData) == FALSE) {
            //outputLastError(_T("SetupDiGetSelectedDevice(hDevInfo, &deviceInfoData) == FALSE"));
            printf("SetupDiGetSelectedDevice(hDevInfo, &deviceInfoData) == FALSE, %d, %x\n", GetLastError(), GetLastError());
        else printf("SUCCESS 2\n");
        // Step 2: For each Monitor: Output Device information
        const unsigned int FLAG_NUM = 30;
        for (int i=0; i<=FLAG_NUM; i++) {
            DWORD buffersize = 0;
            LPTSTR buffer    = NULL;
            while (!SetupDiGetDeviceRegistryProperty(hDevInfo,  &deviceInfoData, flags[i], &dataT,
                                                        (PBYTE)buffer, buffersize, &buffersize))
                if (GetLastError() == ERROR_INSUFFICIENT_BUFFER) {
                    // Change the buffer size.
                    if (buffer)
                    buffer = (LPTSTR)LocalAlloc(LPTR, buffersize);
                else {
                    // Insert error handling here.
            printf("Data: %d: %s\n", i, buffer);
            if (buffer)
Edited by gretty

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Thanks, removing that flag and using "PCI" as the enumerator works now. But I am not sure PCI is the correct enumator value I should be using?


If I want to obtain Device Information for all Monitors, what enumerator should I use? MSDN doesn't list all possible enumerator values.


So far I have tried "Monitor" and "{4d36e96e-e325-11ce-bfc1-08002be10318}" but that causes the same error "data is invalid"


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