How to implement a callback function using LabView's Call Library Function Node?

Question

I am trying to call a fuction from a SDK.dll library using the Call Library Function Node. The SDK was provided to
me and I do not have the source code, just the .dll and .h files.
The SdkSetPropertyEventHandler function has a callback fuction as one of its parameters. How do I implement the
callback using the CLF node? I am a good LabView programmer but this is my first time using the Call Library
Function Node. I have read all the info I can find on NI's web site and the discussion board but cannot figure
this one out. I am using LabView 8.6.
The SDK.h deacribes the function as:
//  Function:   SdkSetPropertyEventHandler
SdkError SDKAPI SdkSetPropertyEventHandler(
            SdkCameraRef                    inCameraRef,
            SdkPropertyEvent                inEvnet,          
            SdkPropertyEventHandler         inPropertyEventHandler,
            SdkVoid*                        inContext );
//  Description:
//       Registers a callback function for receiving status
//          change notification events for property states on a camera.
//  Parameters:
//       In:    inCameraRef - Designate the camera object.
//              inEvent - Designate one or all events to be supplemented.
//              inPropertyEventHandler - Designate the pointer to the callback
//                      function for receiving property-related camera events.
//              inContext - Designate application information to be passed by
//                      means of the callback function. Any data needed for
//                      your application can be passed.
//      Out:    None
//  Returns:    Any of the sdk errors.
A separate header file called SDKTypes.h contains the following data:
typedef  SdkUInt32  SdkPropertyEvent;
typedef  SdkUInt32  SdkPropertyID;
typedef  void       SdkVoid;
typedef  struct __SdkObject*    SdkBaseRef;
typedef  SdkBaseRef    SdkCameraRef;
 SdkPropertyEventHandler
typedef SdkError ( SDKCALLBACK *SdkPropertyEventHandler )(
                    SdkPropertyEvent        inEvent,
                    SdkPropertyID           inPropertyID,
                    SdkUInt32               inParam,
                    SdkVoid *               inContext );
Thanks for your help.
Alejandro
Solved!
Go to Solution.

Answer 1

alejandroandreatta wrote:
I am trying to call a fuction from a SDK.dll library using the Call Library Function Node. The SDK was provided to
me and I do not have the source code, just the .dll and .h files.
The SdkSetPropertyEventHandler function has a callback fuction as one of its parameters. How do I implement the
callback using the CLF node? I am a good LabView programmer but this is my first time using the Call Library
Function Node. I have read all the info I can find on NI's web site and the discussion board but cannot figure
this one out. I am using LabView 8.6.
Basically you do not do that. LabVIEW does not know pointers and certainly not function pointers. What you should do instead is writing a C DLL that implements the callback and also exports a function to be called by LabVIEW that translates between the callback and a LabVIEW user event. Look for PostLVUserEvent() here on the NI site to find examples how to do that.
Rolf Kalbermatter
Message Edited by rolfk on 02-11-2009 08:00 PM
Rolf Kalbermatter
CIT Engineering Netherlands
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