Problem trying to load .dll library using 'loadlibrary', error is, A 'Selected' compiler was not found. You may need to run mex -setup.

I am a beginner on using the loadlibrary function and using .dll files, so I will appreciate any help I can get.

I am trying to load a .dll file with a header file, I am using:

>> loadlibrary('nameoflibrarydll', 'nameofheaderfile')

and it comes up with the error:

??? Error using ==> loadlibrary at 264 A 'Selected' compiler was not found. You may need to run mex -setup.

I do not understand what 'mex' is?

I think a problem is is that the .dll file is written using an old version of Matlab, and it needs to be used using Matlab 2011a. This is so that I can access functions from the header file, the codes of which probably need updating also to run in the new version of Matlab.

I also tried the same line of code for loadlibrary on a different computer and it comes up with the error:

C:\Users\User One\Documents\MATLAB Pentools\Wintab32.dll is not a valid Win32 application.

I understand the problem is to do with 32 bit and 64 bit versions of windows, but I do not understand what this means. If anyone could help explain what all the terminology means and how you think I may be able to proceed with accessing the .dll file, I would be most grateful.

Answer 1

[Friedrich]

Hi,

in order to use loadlibrary you need to choose a compiler. In order to choose a compiler run

mex -setup

This starts a small setup routine in which you select your compiler.

In addition, 32bit ML can load 32bit DLLs only. 64bit ML can load 64bit DLLs only.

How was the DLL generated? I hope not with the MATLAB Compiler, because you shouldn't/can't load ML Compiler generated DLLs in MATLAB. They are not designed to work with loadlibrary and will most likely crash ML.

[hde]

I have used the 'mex-setup' function and selected an option for visual c++ option, however it then came up with the error:

??? Undefined function or variable 'setup'.

after I had chosen which compiler to use.

I then ran the 'mex-setup' command again and got the following output:

>> mex-setup

Usage:

MEX [option1 ... optionN] sourcefile1 [... sourcefileN]

[objectfile1 ... objectfileN] [libraryfile1 ... libraryfileN]

Use the -help option for more information, or consult the MATLAB API Guide.

Y:\MA2051~1\BIN\MEX.PL: Error: No file names given.

??? Undefined function or variable 'setup'.

Would you be able to explain what you mean by 'ML'? I really am a beginner with the terminology.

I am not sure how the dll was generated. I just have a file name with the extension .dll that I am trying to access with the header file.

[Friedrich]

Hi,

ML means MATLAB. Please put a space between mex and -setup, simply copy & paste the command from post into ML.

In addition, ML can pass C header files only. So please make sure you header file is native C code (so no C++ syntax).

For limitations and workarounds see here:

http://www.mathworks.com/help/techdoc/matlab_external/f43202.html#bruzh57-1

[hde]

Yeah, I realised I had missed the space out, thanks.

I think the header file is in C, need to check on that.

Would you be able to say what language the .dll file should be in? I cannot view its contents, just jumbled up symbols.

I now get the error message:

??? Error using ==> loadlibrary at 441

There was an error loading the library

Caused by: Error using ==> loaddefinedlibrary not a valid Win32 application.

I am using a 32-bit operating system, so do not understand this error message in context? In the header file there is a comment line at the start stating that it is a combined 16 and 32 bit version. I thought maybe the 16-bit parts could be causing the problem? If those lines of code in 16-bit were identified and edited to be 32-bit, would that make any sense?

Thanks again!

[Friedrich]

It doesnt matter if the DLL is written in C or C++.

I never saw such a 16/32bit DLL. Not sure if MATLAB can handle this. But this message can also mean that the DLL is a 64bit DLL, since the header talks about 16bit and 32bit I would doubt that.

Can you use the DLL outside of MATLAB? So create a small C/C++ application with calls that DLL. Does this work?

[hde]

That would appear to be a good solution, using the DLL outside of MATLAB. Are you able to recommend any good documentation for creating an application using c or c++ in Visual studio that will allow me to call up functions in Matlab, from Visual studio, which then links to the DLL? I have not used c or c++ before so any hints to go about this would be great?

Thanks for your ideas, I am most grateful.

[Friedrich]

I meant using C/C++ and the DLL only to check if the DLL can be used at all (so no MATLAB involved here). There a several guides in the internet showing you how to use a DLL:

http://www.flipcode.com/archives/Creating_And_Using_DLLs.shtml

Answer 2

[Pang Pang]

In environment, select add-on. Search for MinGW-w64 Compiler and install. Just type in (mex -setup) without the parentheses in the command window once installation finishes.