Use of matlab dlls as third party dependencies

Hi guys,

I am trying to build a Qt application which will generates .mat files. Last year I was using a 32 bits Qt framework and it was working fine. I had two matlab dlls (coming from matlab 2018b if I do remember well) as third party dependencies: libmat.dll and libmx.dll, I could compile and execute my application without any issue.

But the application will frequently use more than 2 Gb of RAM and than is why I am migrating to a 64 bits Qt framework. However Qt is struggling to load matlab dlls. Either a dll is missing or I get the error code 0xc000007b which means that I am using 32-bits and 64-bits dlls.

I already post a question about Qt on their forum but we where not able to find a solution. That is why I am posting the question here.

I have matlab 2022b installed on my machine (Windows x64 bits)

I can see in <matlab_root>/bin/win64 folder the dlls I am looking for: libmat.dll and libmx.dll and I am using mat.h, matrix.h and tmwtypes.h from <matlab_root>/extern/include folder in the source code to interact with the dlls. At that point, I am able to compile (So the matlab libraries are found by Qt) but if I try to start the application, Qt is complaining because some dlls are missing: libmwfl.dll, libmwflstorageutility.dll etc..

Apparently, Qt is also looking in the Windows PATH variable to search for dlls, I had a look in my system path and I can see two paths:

I know this is a matlab forum, not a Qt one, but do you guys have an idea of what I should do to use matlab as a third party dependency ?

Have a nice day,

Pierre-Emmanuel

[埃博拉酱]

I read about your experience on the Qt forum. I think you should construct a minimal reproduction demo and upload it to let us debug it for you.

[Pierre-Emmanuel de Robien]

Hi,

Thank you for answering,

Do you know a matlab dll which has no other dependency so that I can construct a simple demo app ?

Have a nice day,

Pierre-Emmanuel

[埃博拉酱]

You don't need a "runnable" app. What you need is to delete the content from your real project that is not relevant to this issue and send the rest in.

[Pierre-Emmanuel de Robien]

Hi,

I did not forget about the small app to deliver for you to test. I should be able to deliver something today

Thank you again for your patience.

Have a nice day,

Pierre-Emmanuel

[Pierre-Emmanuel de Robien]

Hi again !

I created a simple a Qt console application. As described in the question on the Qt forum, I am using Qt 6.8.1, Qt Creator 15.0.0 and I am using mingw 13.1.0 64 bits.

The goal of the application is to create a .mat file at "C:\Tools\MyMatFile.mat" containing one parameter "MyParameter" containing 6 values for 6 different timestamp.

I have no issue to build, but when running the application, a popup appears saying that a dll was missing. Each time with a new missing dlls. And sometimes I have the 0xc000007b error code.

Good luck for your investigation. If you find something I should change/try, I would be happy to do it !

On my side, I will try to have a cleaned PATH environment variable and add step-by-step only what is mandatory.

Have a nice day,

Pierre-Emmanuel

Answer 1

[Pierre-Emmanuel de Robien]

Hi guys,

I finally figured out why Qt was complaining about missing dlls. When matlab is installed, it adds <matlab_folder>/bin and <matlab_folder>/runtime/win64 to the PATH environment variable. However, the dlls I need to use are in the <matlab_folder>/bin/win64.

By adding this folder to the PATH and now it is working again.

[埃博拉酱]

The magic of building a minimal reproducible demo is not only to help others identify your problem, but more importantly, very often, you will find and solve the problem yourself directly through this process.