Neon_Light

Hello  Rolf,

thank you, you were completely correct. The label was missing.

I did spent a lot of evenings coding and most of it seems to work. To setup the IDE I did use this site it describes how to setup the C environment in VSC and tips how to debug the DLL software.

https://gitlab.com/serenial/talks/11-20-labview-and-vscode-shared-libraries 

I did also try to get rid of the array  changing this code:

typedef struct {
    int32_t status;
    double value;
} DataRecord;

into 

typedef struct {
    int32_t status;
    double value;
} DataRecord, *dataHdl;

......
......

dataHdl handle = NULL;

the rest of the code I did keep the same. This does not work. How can I send one cluster back at a time? Does the handle always need a size even when the size is one cluster / struct? The reason I ask is because the size of the array is different every call, I did find out when using a debug window as described in the link above.

Another question I have is how to transport the  Labview LVUserEventRef data to the callback function? Is the part below legal?

LVUserEventRef giveReftoCallback;


FuncCalledFromLabviw(LVUserEventRef *rwer,int bla)
{
....
giveReftoCallback = rwer;
.....
}


void __stcall MyCallback(....)
{
....
err = PostLVUserEvent(giveReftoCallback, &handle);	
}

You also did write:

Quote

/* if the callback can be reentrant, meaning it can be called while another callback is already executing,
use of a global variable for the data array is NOT safe and needs to be handled differently!!!! */

Yes the callback function will be called ever time there is new measurement data. So I there is a change the callback function is still sending data to Labview when it is called for new data. Is there a easy way to fix this?

thank you for the help!!

Thank you Rolf !! 

but the thing I can still not find is how do I get acces to the array in the event structure. If I wire a number for example index to the create user event it ends up in the event structure. Wile the callback array does not appear. I added a screenshot, hope that helps. 

Hello I  did give it a try I am able to compile some C code send some data to the created DLL and receive data from the DLL. So that is great 🙂 thanks !

The original DLL however will return a array with structs to my C DLL I will try to implement thePostLVUserEvent part there . When I try to make an even structure as an experiment I am not able to get the array out again. This makes me think I am not using the event method in the correct way. what will be the best way to get an array from the DLL back to the Labview event? Do I need to send every array element back with a PostLVUserEvent?

Hello ShaunR, thank you for the answer. I have to admit it was not the answer I hoped for as this will take more time, on the other side learning new things is always a great thing 🙂 . I did read this forum:

And I think for me the most important points are:

Although the document is old I can use most parts of: "Using External Code in LabVIEW". The link to the Ni site contains more recent info: https://www.ni.com/docs/en-US/bundle/labview/page/lvhelp/labview_help.html

One part which is outdated of the external code document is how to set up the environment in the IDE. At this time I am using VSC, as a IDE. Do you have a link to a VSC setup to develop a DLL for Labview? 

12 hours ago, Rolf Kalbermatter said:

Do you have the source code of that wrapper? If so you can modify it, otherwise you will have to create a wrapper around this wrapper or around the original lower level API.

Or maybe that wrapper implements this callback functionality and the lower level API is simply a function API where the caller has to implement its own task handling. In that case it may be simpler to directly go to this lower level API and implement the parallel task doing the logging monitoring entirely in LabVIEW.

Hello Rolf and ShaunR, Thank you for the help!

I do not have the source code of the wrapper but they included 2 files a Typedefs.h and a interface.h

The:

Int LOGEXPORT __sdcall LOG_StartLogging{const char ** logFilename, ptLogCallbackfunction ptFunction, ptObject ptObject}

is implemented in the dll and I can call it with a CLFN, first I tried to wire the output of a Register For Events function to the "ptLogCallbackfunction" as I understood this would provide a function-pointer to a Labview function/vi which would then behave as a callback function. It makes Labview crash though. When the driver is not running it returns a error message. I think the function does not try to use the callback pointer when the driver is not running.

My communication might not be completely correct as I am new to callback functions. Maybe this helps, above example text:

Void __stdcall callbackLog(ptObject object, const int ArraySize, const StructLogdata *const logDataArray)

there is also the text:

typedef Void( __stdcall *callbackLogFunction)(ptObject object, const int ArraySize, const StructLogdata *const logDataArray)

12 hours ago, Rolf Kalbermatter said:

In that case it may be simpler to directly go to this lower level API and implement the parallel task doing the logging monitoring entirely in LabVIEW.

I can give it a try, but how do I approach this?

I can also try to code it in C, think it is interesting and fun but it has been a while since I did code C. Although I planned to refresh my C knowledge, this would take time and focus on one thing to learn at a time might be more successful. It is late now, I will read trough the examples and Using External code pdf tomorrow. Thank you for the help you provided! 

Well the header file I mention is from the wrapper someone else wrote. I have got some functions working from this wrapper. The only part I havent managed to get working is the part with the callback. So what you are saying I need a wrapper to use this wrapper because it uses a callback function? I will read the example you did provide thank you!

Hello I hope someone can help me, I have been trying to get this to work for days but no success yet.

What I want to do

I got a dll with a wrapper, this dll and wrapper can be used for a special datalogger. The wrapper contains multiple functions, I have got some of them working using a CLFN, for instance I can read a jumper setting from the datalogger in LabView. So far everything is fine.

Of course I am not that interested in the jumper setting, I would rather use the datalogger to log data.

I need to run one function to start logging. When there is enough data in the databuffer of the driver dll it will call a callback function I need to write in Labview, here is the function which starts the logging as described in the header file:

Int LOGEXPORT __sdcall LOG_StartLogging{const char ** logFilename, ptLogCallbackfunction ptFunction, ptObject ptObject}

logFilename needs to be a NULL pointer, from my understanding I do not need to do anything with it. Only provide it. If I do not do anything with it some data is saved at a default location.

ptLogCallbackfunction, as far as I know I need to provide a pointer to the callback function

ptObject ptObject, this must be a void pointer

The header also provided how the callback function could look like in 😄

Void __stdcall callbackLog(ptObject object, const int ArraySize, const StructLogdata *const logDataArray)

{

// copy data from logDataArray for use in my code

}

StructLogdata is a struct with different datatypes.

What I did try

I did a search on internet there are some examples about callback functions, most of them point to NET and active X. They use a reg Event Callback. I did read the helpfile at the end of the helpfile there is the text:

“Use the Event structure or the Register For Events function to register and handle non-.NET or non-ActiveX events dynamically” I am having a hard time to find a proper example. I did find this site with some information:

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000000P8XJSA0&l=nl-NL

and this one about the refnum:

https://forums.ni.com/t5/LabVIEW/Passing-Event-Refnum-to-Call-Library-Function/td-p/4107748

So I did make a user event, I wired a static Vi ref containing a callback vi to the input of this user event. I did wire the user event to a Reg event and wired the event registration refnum to the start logging dll call library function node function pointer input and also to an event structure. I did place a counter in the event structure. But nothing happens besides for an exception which makes Labview crash.

The parameters I did use in the call library function are:

logFilename: type numeric, datatype: Signed Pointer-sized int Pass: pointer to value

ptLogCallbackfunction: type: adapt to type, Data format handles by value (tried all options)

ptObject: same as logFilename

I did try a lot of different things. Writing them in this post will result in chaos and I don’t want that. I hope someone can help me with a simple example how to make this work, or point me into the correct direction.

Thank you all for the help!