How to debug generated mex codes

I am trying to build an application in C++ using Visual Studio 2017. I have added paths in the directory as recommended https://www.youtube.com/watch?reload=9&v=vQ5aIxCX3To. Somehow I get an error - libmx.dll not found. I tried following - I copied this dll from bin\win64 and pasted it in the solution directory. After this I got error saying a different dll is missing. Then I tried to copy entire bin\win64 in a different location and added that path. Still the same error. Please help me resolve the issue.

When I generate mex from my code it works just fine, but I can't run the code in Visual Studio-17. Thanks

Answer 1

[Ryan Livingston]

Moved from comment To debug generated MEX code, just pass the -g option to codegen and that will compile a debug MEX file. You can then debug that MEX code by following the same process you'd use for debugging hand-written MEX files:

https://www.mathworks.com/help/matlab/matlab_external/debugging-on-microsoft-windows-platforms.html

In short, you compile and run the MEX in MATLAB and attach Visual Studio to MATLAB, stopping when the MEX code is executed.

Note that the -g option is the same as the Coder config setting EnableDebugging:

https://www.mathworks.com/help/coder/ref/coder.mexcodeconfig.html?searchHighlight=EnableDebugging&s_tid=doc_srchtitle

[Maya Jubran]

Hello

How to actually debug the mex file in the matlab coder . I have built the buildInstrumented mex file successfuly, and following the command line to run the mex file , the error returns to me. What is the full command to enable debugging the mex file ? THank you

Answer 2

[Ryan Livingston]

It sounds like you are generating MEX code. MEX code assumes that MATLAB is present and as a result it may have a large number of dependencies. For this reason, MEX code should be compiled in MATLAB with MATLAB Coder or the MEX command. Compiling it with Visual Studio outside of MATLAB is not recommended.

Instead you can choose one of the standalone code generation options to use inside of Visual Studio. You can do that with:

cfg = coder.config('lib'); % or 'dll'
codegen -config cfg myFunction.m -args ...

and then use that code in Visual Studio. More info on generating standalone code:

https://www.mathworks.com/help/coder/ug/generating-static-c-c-libraries-from-matlab-code.html

Here's an example of using the generated code in Visual Studio:

https://www.mathworks.com/help/coder/ug/use-a-c-dynamic-library-in-microsoft-visual-studio-project.html

Finally, the Deployment category in the documentation may be of interest:

https://www.mathworks.com/help/coder/deployment.html

[PT]

Hi Ryan,

Please let me know if my understanding is correct - it does not make sense to debug a C++ project in VS with mexFunction and all related dependencies included. Instead, a more appropriate process of generating mex from a custom C++ program is to prepare the C++ code using whatever compiler, then put the mexFunction and all dependencies and then generate mex. The recommendation is to not debug C++ codes within Visual Studio after mexFunction is in place.

I can already generate mex code and use it in Matlab - that is not an issue. My problem is - I need to debug my custom C++ code using Visual Studio. When I try to run my code within VS I get an error - libmx.dll not found which I am unable to fix. I hope this explanation is better than my original question.

-PT

[Ryan Livingston]

Got it. That helps. Just pass the -g option to codegen and that will compile a debug MEX file. You can then debug that MEX code by following the same process you'd use for debugging hand-written MEX files:

https://www.mathworks.com/help/matlab/matlab_external/debugging-on-microsoft-windows-platforms.html

In short, you compile and run the MEX in MATLAB and attach Visual Studio to MATLAB, stopping when the MEX code is executed.

Note that the -g option is the same as the Coder config setting EnableDebugging:

https://www.mathworks.com/help/coder/ref/coder.mexcodeconfig.html?searchHighlight=EnableDebugging&s_tid=doc_srchtitle

If that helps, would you consider changing the title of this question to something like "How do I debug MATLAB Coder MEX files?" so that others could find it?

[PT]

The second link is very helpful, and answers my high level question. If you think its appropriate you could move your comment into a new answer, so that it can be accepted.

Thanks

PT