How I solved Matlab/Simulink S-Function error: mexa64: GLIBCXX_3.4.xx not found

Invalid MEX-file '/home/user/mysfunction.mexa64': /opt/matlab/R2025a/bin/glnxa64/../../sys/os/glnxa64/libstdc++.so.6: version `GLIBCXX_3.4.32' not found (required by /home/user/mysfunction.mexa64)
```plaintext {filename="mysfunction.mexa64"}

## Solution

This error occurs because the version of `libstdc++.so.6` that Matlab is using (`/opt/matlab/R2025a/sys/os/glnxa64/libstdc++.so.6` in this case) is older than the one required by the compiled S-Function (which is used during compilation with `mex`).

In my case, Matlab comes with `GLIBCXX_3.4.30` but my system libstdc++ is `GLIBCXX_3.4.32`. This is a very minor mismatch, the system library is ever so slightly newer (Ubuntu 24.04 LTS, 2025-08-06).

I resolved this issue by **deleting the `libstdc++.so.6` file in the Matlab directory** since it works just as well with the system's `libstdc++.so.6` file.

**Before attempting this solution, ensure you have a backup of the original file.**

```sh {filename="remove_matlab_libstdc.sh"}
rm /opt/matlab/R2025a/sys/os/glnxa64/libstdc++.so.*
```plaintext {filename=".so.6"}


After that, you need to restart Matlab and also recompile your S-Function using `mex`. The error  should have been resolved after that.