How to deal with the C++ Callback function in Labview

[RogerLu]

I am tring to get the image data from a Video Capture card. The SDK is a DLL and an .h file. I met some problems when I am using the Call Library Function Node for a function. The function was described like this:

Function Name: int RegisterStreamDirectReadCallback(STREAM_DIRECT_READ_CALLBACK StreamDirectReadCallback, void* Context)

Parameter: STREAM_DIRECT_READ_CALLBACK StreamDirectReadCallback

                  void* Context

Callback function explanation:

typedef int (* STREAM_DIRECT_READ_CALLBACK)(ULONG channelNumber, void * DataBuf,DWORD Length, int FrameType,void *context);

 ULONG channelNumber               channel number

 void* DataBuf                                  buffer address

 DWORD Length                              buffer length

 int FrameType                                 buffer type

 void* context                                   device context

so how can I define the parameters in the Call Labrary Function Node for this ? 

[The_Chancenator]

Hi Roger,

I'd recommend taking a look at this community example, Calling C/++ DLLs Containing Simple and Complex Data Types from LabVIEW

I'm most concerned about the DWORD data type--what errors does it throw when you try to get the DLL to work with it or what performance are you seeing?

[nathand]

This is a commonly-asked question, and the recommended approach is to write a small DLL in C with the callback, and use that callback to trigger an event in LabVIEW.  There are many posts in this forum on this topic; try a search for "callback dll."