Linking MATLAB to a DLL library

Question

I am trying to execute some example code from a MATLAB toolkit, 'oscmex'. This toolkit allows for communication using the OSC protocol over MATLAB. I presume this question is non-specific; it should apply to any toolkit that is set-up in the manner that this one is.

Reasons aside, I'm having some simple trouble getting the toolkit up and running. The toolkit comes with no documentation whatsoever; just a set of six DLL files (in one directory), and a set of four MATLAB '.m' example code files (in another directory). Every toolkit I've used in the past has either been a built-in kit or has had an intuitive (semi-automated) install procedure.

After downloading the toolkit, the first thing I tried was to simply run one of the '.M' example codes. This failed as the first line of the code contained the function osc(), which is not (currently) recognised by MATLAB.

So, I figured maybe I need to move the '.M' files into the same folder as the DLLs; perhaps MATLAB would see the functions inside the DLLs. No dice.

So, I realise that I have to somehow link MATLAB to the DLLs on startup. I tried adding the DLLs to a folder and adding an entry to that in the 'pathdef.m' file. This also failed.

I've read somewhere I can load a DLL file by using the loadlibrary() function. So, I tried doing this for the DLL files. This failed on the first file:

>> loadlibrary('osc_free_address.dll')

Error using loadlibrary>lFullPath (line 587)
Could not find file osc_free_address.h.

I'm starting to run out of options... How can I get this set of DLLs up and running?

Answer 1

Try changing the extension from .dll to .mexw32 (in win32), or .wexw64 (in win64). It's a long shot but it might work.

Answer 2

The Shared Libraries cannot be used directly. As you have mentioned, you need to load them into MATLAB using loadlibrary. According to the documentation, loadlibrary takes two arguments (at least). The first argument is the name of the file, and the second one is the header file which contains definition of functions and external variables. If you do not provide the header file, the MATLAB looks for the a file with the same name as the DLL. Having said that, you need to have access to the header file or at least if you know how the function looks like, you need to write a header for the DLL.

I have worked with the DLLs in MATLAB. The MATLAB is not very user-friendly as long as DLL is concerned. Especially, if the DLL is written in a language other than C (or C++) you will have trouble loading the function into MATLAB.

Besides, MATLAB can only support some specific DLLs. Based, on your version of MATLAB, you need to find out whether or not the shared library is supported by MATLAB. Have a look at Here

In a nutshell, it is not easy to load a DLL into MATLAB. You need to have some information from DLL.

Answer 3

If you look at the build for that software, it is compiling mex files, not DLLs (shared libraries): http://sourceforge.net/p/oscmex/code/4/tree/trunk/src/osc_make.m.

I would try using the mex commands instead of the dll commands (perhaps the files are just misnamed.) Even better, I would compile the files yourself with mex using the build file in source.

Note that the instructions also say that you need liblo-0.22 in order to run the library, so make sure you have that accessible as well.

Answer 4

I took a look at your OSC Toolkit. It seems they have been compiled by MATLAB mex. But, it is not mentioned for which kind of architecture they have been built. You can type mexext at MATLAB command prompt to find the extension for your MATLAB mex files. Then, change the DLL extensions to the given extension. If the original mex is compatible with your matlab, the DLL can be easily accessed by MATLAB. Just make sure to add the folder to your MATLAB path.

Answer 5

Browsing this library's web page it would seems these DLLs are just old form of mex files.
Therefore, they should not be used in the context of shared library (e.g., using loadlibrary and calllib), but rather compiled directly to mex files.

To do so, I would suggest the following steps:

1. Make sure you have a working mex compiler configured for your Matlab.
   In matlab, type:

   >> mex -setup
   

   this will guide you through the configuration process. I understand that you are working on a windows machine, I usually work with visual studio compiler - works best for me.

2. This library's README file suggests that OSC

   requires liblo 0.22 or later. See http://plugin.org.uk/liblo/

   Make sure you have this library and it is located in you LD_LIBRARY_PATH (see e.g., this question for details, or the mex docs).

3. Get the source code for OSC library from their repository.

4. Compile the sources in matlab using

   >> mex -O -largeArrayDims osc_free_address.c
   >> mex -O -largeArrayDims osc_free_server.c
   

   and so on for all 7 c source files. After mex-ing the c files you'll have mex files that you can run from Matlab as if they were regular functions.
   You may find it useful to use the library's make file, as suggested by Andrew Mao.

Good luck,