Calling Dlls from LabVIEW

[FightOnSCTrojan]

LabVIEW Gurus:

I am working with some software engineers who have no experience in LabVIEW. Unfortunately I have little experience in C/C++ to make sense of their inquiry.  

Basically we are dealing with “Data Marshalling”. I will call a DLL and issue a command (string) and get back a 2-D array and an integer. So far so good.

The C/C++ programmer requested that I provide them with a pointer/memory address in which they will store data, so I can read it once the dll returns the array and integer. I browsed through the example online http://decibel.ni.com/content/docs/DOC-1690 and thought that if I wanted to read from the dll, the process is a simple as calling the appropriate function and configure the parameter (no pointers needed).

So, is there a specific way that they need to write the C/C++ code to be used in LabVIEW? Or what else to I have to take into consideration?

Thank you,

Santiago  

[smercurio_fc]

That example is pretty simplistic as it only deals with integers. In this case no pointers are required since everything is returned by value. When you're dealing with arrays, however, you need to deal with pointers. If you open the Example Finder (Help -> Find Examples) and search for "dll" you will see the "Call DLL" example. That contains many examples of how to call DLL functions with a wide variety of datatypes. I strongly suggest looking at that example. There is also a chapter in the LabVIEW Help on calling DLLs (Fundamentals -> Calling Code Written in Text-Based Progamming Language).

You have 2 things to consider:

• You're dealing with arrays - this means you typically need to pre-allocate the memory in LabVIEW, and it sounds like that's what the DLL expects you to do. This amounts to using the Initialize Array function to create your 2D array of the appropriate size and datatype.
• You may be dealing with a C++ DLL. LabVIEW can only interface to C DLLs. This doesn't mean that you can't create a DLL in C++, but it does mean that the C++ programmers need to add an extern "C" modifier to the function calls, otherwise you get name mangling, and LabVIEW won't be able to call the DLL. The DLL programmers should know what that means.