question

These problems are quite often caused because of mismatches in the header files, which is the case here. Specifically, with 2017 we made several changes to the Variant class, such that if you have a 2016 header defining Variant (datatypes.h), it will not return correctly because the 2016 Variant is different than the 2017 Variant.

Obviously, we can do a better job of keeping the dll maker repository up to date. However, you can usually fix this on your own without having to wait for us to update the dll maker repository. The way I usually do it is by doing a diff analysis on my project's headers relative to the headers in the installed version. I use WinMerge, and I compare my project directory with <FlexSim-Install-Directory>\program\system\include\. I don't move any new headers into my dll project. I only copy existing headers with differences to my dll project.

When we initially made the dll maker repository available, we made it with the idea that it would be forward-compatible with future versions. Unfortunately, that is no longer the case, specifically because functions can now return Variant, a non-primitive class that may need tweaks and changes over time. In my opinion the ability to return a Variant, and with that arrays, strings, nodes, etc., outweighs the downside of having to update headers. Perhaps Variant changes will settle over time such that header updates are not required as often. However, for now we advise you to update headers at least with each feature release of FlexSim.