Something wrong with _UCharPos

[RhoSigma]

UCharPos is in the repo, but not in 3.7.  It was added after 3.7 was released and is still just part of the development build.  Clone the repo and you can test it, or else wait for it to go live in 3.8+.

Or v3.7.1 at least, as the Wiki states under the Availability Section of _UCHARPOS.

You can always get the latest development build here: https://github.com/QB64-Phoenix-Edition/QB64pe/actions

Click the latest available "Automatic update of ./internal/source" (usually at the top), on the loaded page scroll to bottom and download the desired package from the "Artifacts" section.