mex failing to compile function

Hi.

I'm trying to compile functions previously compiled with mex in MATLAB

>> mex Cbetabinornd.cpp

Now gives the following error message:

Renamed options file '/Users/lfslbx/Library/Application Support/MathWorks/MATLAB/R2025b/mex_C++_maca64.xml' to '/Users/lfslbx/Library/Application Support/MathWorks/MATLAB/R2025b/mex_C++_maca64_backup.xml'.

Building with 'Xcode Clang++'.

Error using mex

Undefined symbols for architecture arm64:

"_mexCreateMexFunction", referenced from:

<initial-undefines>

"_mexDestroyMexFunction", referenced from:

<initial-undefines>

"_mexFunctionAdapter", referenced from:

<initial-undefines>

ld: symbol(s) not found for architecture arm64

clang++: error: linker command failed with exit code 1 (use -v to see invocation)

If I use the -v option there is a lot of information, I can paste it here if required.

I think this has happened since my last MacOS upgrade (to Sequoia 15.7) and/or xcode command line tools update (clang++ version 17.0.0).

I have tried uninstalling and reinstalling the xcode command line tools and have installed MATLAB 2025b (it was failing on 2023b also).

Any suggestions welcomed.

Thanks.

Answer 1

[Ron Crump]

The two .cpp files in question were using the C API. We have recoded them to use the C++ API and they now compile.

[Bruno]

The problem seems to be caused by a bug in the latest version of xcode command line tools. For those who can't (or don't want to) switch to the C++ API, a temporary workaround is to pass the -ld_classic flag to the linker. When using the mex command, the right invocation should be something like

mex LINKFLAGS='$LINKFLAGS -ld_classic' source.cpp

[Ron Crump]

Thanks, Bruno. Good to know.

[Robert]

Thanks Bruno, fixed my problem with this message as well, for now.

FYI, on my 2024b LINKFLAGS didnt' work, I had to use LDFLAGS

also note the: ld: warning: -ld_classic is deprecated and will be removed in a future release