Communicating with a GPS Device

You can use the methods of the IPosNav interface to communicate with a GPS device.

    To communicate with a GPS device

1. Initialize COM and obtain a handle to an IPosNav interface.

   The following code example shows how to do this:

   HRESULT hResult = CoCreateInstance(CLSID_PosNav, NULL,
                                      CLSCTX_INPROC_SERVER, IID_IPosNav, 
                                      (LPLPVOID) &pPosNav);
   

2. Call FindDevices to obtain a list of installed GPS devices, then select a device to use.

   The following code example shows how to do this:

   hres = pPosNav->FindDevices(&pDevice, &dwNumDev);
   if(FAILED (hres) || dwNumDev == 0)
     {
     pPosNav->Release();
     // Insert error handling here.
     }
   
   // Call your selection function to choose one device.
   PNDEVICE *pDeviceOfChoice = MySelectDevice(pDevice);
   

3. Call OpenDevice to open the selected device for communication.

   The following code example shows how to do this:

   hres = pPosNav->OpenDevice(&hPNAPI, pDeviceOfChoice);
   

4. Call DeleteDeviceList to delete the device list after the selected device is open.

   The following code example shows how to do this:

   pPosNav->DeleteDeviceList(pDevice);
   if(FAILED (hres))
     {
     g_pPosNav->Release();
     // Insert error handling here.
     }
   

5. Call StartCall to retrieve data from the device.
6. Call CloseDevice to close the device.

   The following code example shows how to do this:

   hres = pPosNav->CloseDevice(hPNAPI);
   // Release the interface.
   pPosNav->Release();