Simple C Cross-Platform Shared Code (Non-DLL) Call Library Function Example

[Kravlor]

I am a graduate student in the fusion science community and am currently developing a transition of our group's data storage system to MDSPlus, the de facto fusion research archival system. This involves getting LabVIEW to write results of our various measurements to a MDSPlus data source. The MDSPlus libraries come pre-packaged with LabVIEW VI's that are essentially wrappers around a Windows DLL. Since our group has LabVIEW running on Windows, Macintosh, and Linux machines, I am in the process of generating the functional equivalent of a DLL for use with the built-in Call Library Function node.

With that motivation in mind, I found that the available documentation regarding how to build these shared libraries was somewhat lacking (especially with regard to OS X) and was unable to find any real examples of how to go about building one with the standard Linux/OS X build tools of GCC and Make. After engaging in an email discussion with NI engineers, I was able to write a simple, Mac OS X and Linux compatible example of a C shared library that is built using only GCC and Make in a manner such that LabVIEW will recognize it, a C application that links against it, as well as a LabVIEW VI that demonstrates calling the C library with the Call Library Function node.

Here's the relevant information that was gleaned from emailing NI: LabVIEW recognizes shared libraries via the following methods, depending on OS: .dll file extension (Windows), .so file extention (Linux), and a proper .framework directory/symlink structure (Mac OS X). I figured it was worth posting up here so people can search for it unlike I was able to!

For those of you interested in implementing cross-platform libraries that can be called through LabVIEW, you can take a peek at my example, which should be attached to this message. I've released it under the GPL. (I'd submit it to the Code Library, but for some reason the file uploading dialogue doesn't like the '/' characters in the directory specification provided on Linux and OS X!)

[Wiebe@CARYA]

Hi,

Is there anything in the labview code that needs to be changed when you change platform? E.g. is the Call Library Node configuration the same on each platform?

Regards,

Wiebe.
"Kravlor" <x@no.email> wrote in message news:182203@exchange.ni.com...
I am a graduate student in the fusion science community and am currently developing a transition of our group's data storage system to MDSPlus, the de facto fusion research archival system. This involves getting LabVIEW to write results of our various measurements to a MDSPlus data source. The MDSPlus libraries come pre-packaged with LabVIEW VI's that are essentially wrappers around a Windows DLL. Since our group has LabVIEW running on Windows, Macintosh, and Linux machines, I am in the process of generating the functional equivalent of a DLL for use with the built-in Call Library Function node.<br><br>With that motivation in mind, I found that the available documentation regarding how to build these shared libraries was somewhat lacking (especially with regard to OS X) and was unable to find any real examples of how to go about building one with the standard Linux/OS X build tools of GCC and Make. After engaging in an email discussion with NI engineers, I was able to write a simple, Mac OS X and Linux compatible example of a C shared library that is built using only GCC and Make in a manner such that LabVIEW will recognize it, a C application that links against it, as well as a LabVIEW VI that demonstrates calling the C library with the Call Library Function node.<br><br>Here's the relevant information that was gleaned from emailing NI: LabVIEW recognizes shared libraries via the following methods, depending on OS: .dll file extension (Windows), ..so file extention (Linux), and a proper .framework directory/symlink structure (Mac OS X). I figured it was worth posting up here so people can search for it unlike I was able to!<br><br>For those of you interested in implementing cross-platform libraries that can be called through LabVIEW, you can take a peek at my example, which should be attached to this message. I've released it under the GPL. (I'd submit it to the Code Library, but for some reason the file uploading dialogue doesn't like the '/' characters in the directory specification provided on Linux and OS X!)


addOne.tar:
http://forums.ni.com/attachments/ni/170/105985/1/addOne.tar

[Kravlor]

In this example, the VI is left intentionally broken. The Call Library Function node needs to be edited so that LabVIEW knows where you built the addOne library libAddOne.[so/framework]. Aside from the location of the shared library, there shouldn't be any other changes, since the idea is to have the same function (long addOne(long a); ) be called across multiple platforms. The README file included with the distribution mentions this, as well as how to build the library on the Mac or Linux.

If you wanted to set up the Call Library Function node from scratch, you'd need to look at addOne.h to examine the exported functions available in the library and their parameters; on Linux and Mac it doesn't seem like the configuration window for the Call Library Function node is capable of displaying the list of functions that is available in a drop-down menu. (On Linux I believe that is a 'feature,' but I haven't seen documentation claiming the Mac isn't capable of this; does anybody here know if the Mac can sort through the available functions LabVIEW can call in a shared library?)