Call engOpen in C code, launch functionnal matlab engine but hangs on C process

Hello, I'm testing matlab engine library with engdemo.c exemple.

Compiling the code directly with gcc:

$ export LD_LIBRARY_PATH="matlabroot/bin/glnxa64"

$ mv matlabroot/sys/os/glnxa64/libstdc++.so.6 matlabroot/sys/os/glnxa64/libstdc++.so.6.old (get rid of the clunky matlabroot/sys/os/glnxa64/libstdc++.so.6 in a dirty way and use /usr/lib/x86_64-linux-gnu/libstdc++.so.6 instead)

$ gcc -o engdemo -L matlabroot/bin/glnxa64 -lmx -leng -lm -lmex -lmat engdemo.c -Imatlabroot/extern/include

But when I run the executable, it calls engOpen(), launch a matlab command window but then hang inside the function. If I manually quit the matlab command window engOpen release the process but return NULL.

Thanks for your help!

EDIT: explicit "get rid of the clunky matlabroot/sys/os/glnxa64/libstdc++.so.6 in a dirty way and use /usr/lib/x86_64-linux-gnu/libstdc++.so.6 instead" sentence with the command used.

[Yongjian Feng]

Not sure what you meant by "(get rid of the clunky matlabroot/sys/os/glnxa64/libstdc++.so.6 in a dirty way and use /usr/lib/x86_64-linux-gnu/libstdc++.so.6 instead)", and why you need that. Does it work if you don't do that?

[Nathan Arbeid]

I rename libstdc++.so.6 to libstdc++.so.6.old.

If I don't, here is the link error I get:

```

/usr/bin/ld: /opt/Matlab/R2020b/bin/glnxa64/../../sys/os/glnxa64/libstdc++.so.6: __cxa_thread_atexit_impl: invalid needed version 48

/usr/bin/ld: /opt/Matlab/R2020b/bin/glnxa64/../../sys/os/glnxa64/libstdc++.so.6: error adding symbols: bad value

collect2: error: ld returned 1 exit status

```

And when I said that the linker use /usr/lib/x86_64-linux-gnu/libstdc++.so.6, it is speculation, I did not verify.

[Yongjian Feng]

Again, not a good idea. You renamed the libstdc++ shipped with matlab to force the process to use the system libstdc++. This will force matlab to use that lib as well. It can cause trouble.

[Nathan Arbeid]

Ok do you have suggestions to resolve this issue in a cleaner way ?

Answer 1

[Nathan Arbeid]

My hang issue was resoleved by setting the environement variable $PATH

export PATH=matlabroot/bin:$PATH

as suggested here https://fr.mathworks.com/help/matlab/matlab_external/run-linux-engine-application.html

But do not understand why.