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Do I need Developer studio (C++ programming language) in my computer when I call a dll through my labview?

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@yemin wrote:

" make sure to configure the additional 4th parameter to be passed by reference (Pointer to Value)."


I didnt understand this. I have 4 parameter one of them is return value, other 3 are inputs. which one is the Additional 4th parameter..Do  i need to add one more or change one of those to pointer to value?




Well look again at the two function prototypes I pasted. The Call Library Node is setup to return the value as function return value and has three parameters. The C function in the DLL is setup to have no (void) return value and 4 parameters, with the forth being by reference (the & in front of the parameter name, which by the way is C++ only, in C you always have to use the * (star) to signify a pointer, which a reference value is too.


You must make the C function declaration match the function prototype shown in the Call Library Node in the number of parameters and parameter types or you create rubish. Since the C function does not return any value, but your Call Library Node tries to retrieve a value from the A register which is used to return function values, you receive some garbage, which is interpreted as NaN, but really could be anything.


One of the options in the Call Library Node configuration is to specify that a parameter is to be passed by Value (your first three function parameters) or as Pointer (the 4th and last parameter).


That the number of parameters should be correct between caller and callee is however sooooooooooo basic C knowledge, that I would suggest to you to first study a beginners course for C before you dig deeper into using the Call Library Node independant of the C compiler you use.

Rolf Kalbermatter
Averna BV
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Message 31 of 48


Thank you Nlquist and Rolf, I am happier now 🙂 it worked finally at the labview and made calculation  when I changed the void to double in the code like this;



extern "C" __declspec(dllexport)double BoxProperties(double L, double H, double W);



Rolf, thank you for advice, my situation is kinda tough cause I should finish this work at the end of this month and the problem is its the first time I am using C++ builder and labview as well. I know its ridiculus and thats why I am bothering you too much....


I think I am gonna try to make dll in C++ builder by trial and error...Because code is much longer than above calculation and I dont exactly know where do I need to put that extern "C" __declspec and "int WINAPI...." stuff.....


In the long code there is a  notepad outfile is created when i run it in C++ builder .. So I dont have one return type. it means I need to leave return type "void" in the parameters and if my DLL is okey, labview creates that out.txt directly??


Thank you again..... 


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Message 32 of 48

Congratulations!  I guess I should have mentioned this earlier but I forgot that there is a DLL import wizard that will create CLFN VIs from your C++ code automatically....  Maybe. Smiley Wink


Tools > Import > Shared Library (.dll) will open the wizard.  You have to identify your C code (and header) files and then it will try to analyze your files and create VIs with icons, error-handling, etc.  Note that I said "try"!  It's NOT magic but it has worked for me when converting big libraries of C++ functions into LabVIEW VIs which was a BIG time saver.  Try it on your DLL and see what you get...


WARNING:  If you have the Report Generation Toolkit you must un-install it first or it will cause the DLL wizard to lock up.  (unless NI has fixed that bug)

LabVIEW Pro & Measurement Studio Pro (VS Pro) 2019
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Message 33 of 48

Thanks NIquist,


I am trying to use Import Shared Library, but it asks me to add dll and  header file but I dont have a file with .h extension.  

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Message 34 of 48

Yes, it's really designed to convert big C++ libraries that would have header files.  Keep it in mind for the future though...

LabVIEW Pro & Measurement Studio Pro (VS Pro) 2019
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Message 35 of 48


Thanks again friends....


Finally I could create a text for my simple calculation. Results in the text file is correct . However although labview creates the text file, it shut down immediately and give the attached errors. Do you have an idea about that..



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Message 36 of 48

Reading your latest few posts I get a feeling of why? Let me explain to you:


1) Your C code obviously is a self contained executable and was never meant to be called as library, otherwise you would have a proper header file for all the functions that the library exports. So you have to go through your entire code and find all the relevant functions and add the extern "C" and declspec(dllexport) to all functions you want to export from the DLL.


2) Your DLL does also create files, possibly at some fixed location that can't even be changed by the calling application. Personally I would always prefer to create the output files in LabVIEW and simply only do the "complicated" calculations in a DLL.


3) What you have shown so far doesn't look particularly complicated. I really wonder if your time wouldn't have been better spent learning to understand what the C code does and then porting it all to LabVIEW. One important question in this respect is how many SLOCs (source line of codes) are we talking about in this C code? Unless it is already a well designed library you won't get away without studying the code anyhow in depth to be able to export the right functions and interface them to LabVIEW, but then you have already done most of the hard work to reimplement them in LabVIEW. If we talk about many tenthousends of SLOCs then maybe going through all the DLL import pericles could be a faster way of solving this problem, but if it is a moderately sized C code, converting everthing to LabVIEW is likely faster and much easier to debug when you integrate it into an application. Debugging a DLL directly from within LabVIEW is always an additional hassle and your use of C Builder is likely another obstacle in doing source code debugging in DLL code called from LabVIEW.


4) The error you get after calling your function most likely is caused by some illegal action in your C code. What it is? Well without looking at the source code I could just as much guess it has to do with the position of the moon when you call that code. But then I don't really feel like reviewing some less than impressive code either! The error might always have existed but if it was just a single start up once executable, shoot once and then die anyhow after creating the result file, it may never have surfaced to the Windows user. Or it could be something you did to make the code callable from LabVIEW, such as exporting the functions you thought you needed in LabVIEW but not initializing memory buffers used in those functions and originally initialized in the main function of your original program.


In short I do really wonder hard if you would not already have a fully working solution if you simply had ported everything to LabVIEW and forget about creating a DLL and trying to import it into LabVIEW.

Rolf Kalbermatter
Averna BV
Message 37 of 48



   Rolf, actually my code is not very long I think....probably it is around 200 lines. You are right, it would be much easier if we directly write the code in labview but I couldnt convince the bosses. They want it with dll :(...



   I am attaching two pictures. First one is beginning of the code that I made dll. As you see, I added "extern stuff" with the input declarations. After that variable declarations were made


  Also, second attachment is beginning of the main program which is at the end of the code (bottom). I added same input in the paranthesis....



  When I run it like it, Labview creates the output text file. However there is no calculation in it....I think it doesnt make the calculations for a reason..I have no idea for the reason.. I feel like if I add something else, it is gonna calculate 🙂



   Thank you again for your help and patience....



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Message 38 of 48

Well all I can say to this is: The powers in your case are making things triple complicated and should be replaced.


As to your problem: Oh well, those JPG images show absolutely nothing relevant so no joy there.

Rolf Kalbermatter
Averna BV
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Message 39 of 48


@yemin wrote:


However although labview creates the text file, it shut down immediately and give the attached errors. Do you have an idea about that..

In response to this, have you tried to copy and paste your VI into a new VI?  It is possible that you have a corrupted Call Library Function node.  If this doesn't work and since your VI is not very large, you could try to recreate the VI from scratch.  Finally, you could try repairing your install.  To do this, you will have to go into your Control Panel and then Programs and Features.  From there, click National Instruments Software and select Unistall/Change.  From there, choose LabVIEW <version> and select Repair. 


I hope this helps!


Kim W.


Applications Engineer
National Instruments
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Message 40 of 48