Enumerating System Devices

Use the IWiaDevMgr::EnumDeviceInfo (or IWiaDevMgr2::EnumDeviceInfo) method to enumerate the Windows Image Acquisition (WIA) devices installed on a system. This method creates an enumeration object for the properties of the devices, and returns a pointer to the IEnumWIA_DEV_INFO interface that the enumeration object supports.

You can then use the methods of the IEnumWIA_DEV_INFO interface to obtain an IWiaPropertyStorage interface pointer for each device installed on the system.

The following code from the WiaSSamp sample application demonstrates how to create an enumeration object for the devices on a system and iterate through those devices:



    HRESULT EnumerateWiaDevices( IWiaDevMgr *pWiaDevMgr ) //XP or earlier
    HRESULT EnumerateWiaDevices( IWiaDevMgr2 *pWiaDevMgr ) //Vista or later
    
    {
        //
        // Validate arguments
        //
        if (NULL == pWiaDevMgr)
        {
            return E_INVALIDARG;
        }

        //
        // Get a device enumerator interface
        //
        IEnumWIA_DEV_INFO *pWiaEnumDevInfo = NULL;
        HRESULT hr = pWiaDevMgr->EnumDeviceInfo( WIA_DEVINFO_ENUM_LOCAL, &pWiaEnumDevInfo );
        if (SUCCEEDED(hr))
        {
            //
            // Loop until you get an error or pWiaEnumDevInfo->Next returns
            // S_FALSE to signal the end of the list.
            //
            while (S_OK == hr)
            {
                //
                // Get the next device's property storage interface pointer
                //
                IWiaPropertyStorage *pWiaPropertyStorage = NULL;
                hr = pWiaEnumDevInfo->Next( 1, &pWiaPropertyStorage, NULL );

                //
                // pWiaEnumDevInfo->Next will return S_FALSE when the list is
                // exhausted, so check for S_OK before using the returned
                // value.
                //
                if (hr == S_OK)
                {
                    //
                    // Do something with the device's IWiaPropertyStorage*
                    //

                    //
                    // Release the device's IWiaPropertyStorage*
                    //
                    pWiaPropertyStorage->Release();
                    pWiaPropertyStorage = NULL;
                }
            }

            //
            // If the result of the enumeration is S_FALSE (which
            // is normal), change it to S_OK.
            //
            if (S_FALSE == hr)
            {
                hr = S_OK;
            }

            //
            // Release the enumerator
            //
            pWiaEnumDevInfo->Release();
            pWiaEnumDevInfo = NULL;
        }

        //
        // Return the result of the enumeration
        //
        return hr;
    }


WIA_DEVINFO_ENUM_LOCAL is a WIA constant that represents the only valid value for this parameter.

In the example, the parameter pWiaDevMgr points to an instance of the IWiaDevMgr (or IWiaDevMgr2) interface after a previous call to CoCreateInstance.

The application calls the IWiaDevMgr::EnumDeviceInfo (or IWiaDevMgr2::EnumDeviceInfo) method of the IWiaDevMgr (or IWiaDevMgr2) pointer pWiaDevMgr that fills pWiaEnumDevInfo with the address of a pointer to the IEnumWIA_DEV_INFO interface.

If the call succeeds, the application then calls the IEnumWIA_DEV_INFO::Reset method of the IEnumWIA_DEV_INFO pointer. The pWiaEnumDevInfo variable ensures that the enumeration starts at the beginning.

If this call succeeds, the application iterates through the devices on the system by repeatedly calling the IEnumWIA_DEV_INFO::Next method of the IEnumWIA_DEV_INFO pointer pWiaEnumDevInfo until the method no longer returns S_OK, indicating that the enumeration is complete.

Each call to pWiaEnumDevInfo->Next fills pWiaPropertyStorage with a pointer to the IWiaPropertyStorage interface that contains property information for a specific device.

 

 

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