@Tyri wrote:
Hi,
@cordm wrote:
From a first glance, serverURIs is passed as LabVIEW handle and binarypwd_len is a u8 instead of i32. That will not work.
Oh yes, the binarypwd_len was wrong. But what do you mean with the serverURIs? I thought I copied it more or less from here.
For a test I have replaced the serverURIs now just with a U32-0 (NULL pointer) and corrected the binarypwd_len but I still get the error. I still would like to know the source of this problem, but maybe it is not needed anymore:
You did, but then you put it in a cluster. Arrays in a cluster will be passed as LabVIEW handles and there is no way to turn that off. You would need to create another pointer, write your array into it and put the pointer in the cluster. That might be fine for a single function, but there are more nested structures in other functions.
@cordm wrote:
I do not think you can interface to that library with any reasonable effort in pure LabVIEW. You are better off writing a wrapper.
You are using the async version. How are you going to implement the callbacks to get data back into LabVIEW?
Yes, you are absolutely right. I just have not thought about that.
So I guess the correct way would be to write a C dll which collects the returning answers (and everything else) in a queue or so and poll it from LabVIEW? (Or I think I have an example somewhere where a LabVIEW queue is passed to the dll for a similar purpose - I just have to check the C code for that).
And in that case, since I nevertheless have to go through the wrapper I can simplify the parameter list of the connect function from above.
So thanks a lot for bringing that up.
Greetings Dennis
As far as I know, queues are not documented for external libraries. The way to go is to use user events by calling PostLVUserEvent. Knowledge Base: Provide a Callback Function Pointer to My DLL Using LabVIEW
In LabVIEW, you define a user event, pass it to the dll and call PostLVUserEvent with data matching the event. I am not sure how memory management works for that function. I allocate anything that is not a primitive with the Memory Manager functions ands dispose the handles after making the call. That seems to work.
You will need some way to get to the event refnums when the callback functions are called. The easy way is a global variable in the dll, but that is not thread-safe.
The callbacks get a pointer to a freely definable "object". That pointer is assigned in the connectOptions struct. Allocate a struct in your wrapper where you put the LVUserEventRefs (not their pointers!). You need to keep track of that pointer for the lifetime of the client and deallocate it when you free the client.
