The software linked by lastchance is an extension for R statistics application: https://www.r-project.org/
If that is the "R" in:
"The R core team notified us that they're removing C header file S.h from R."
then you should search the code of R for that file "S.h".
When you have found the "S.h", then you can read from it what it provides.
The next step is to identify what in your "C file" depends on those provided features.
You could obviously just comment out that include, compile, and note the errors. Then look into S.h to find out what those needed bits are and figure out an alternative way to do them.
@an8877,
I'm not sure why you edited your post to remove the name of the groHMM software - it would have enabled us to have a look in the source code there.
I agree with @keskiverto - it is probably to do with interfacing the C/C++ code to code written in R. According to one of the manuals in @keskiverto's link:
So, try just commenting it out and seeing what happens when you try to compile the code: quite possibly nothing, as the source code for that software seems to have the more up-to-date header <R.h> include'd as well. Failing that, just replace <S.h> with <R.h> and see what happens.
Well, somebody must have deleted the OP's post. Did they actually edit it to put spam in it?
From the dates (and reduced content), the stackoverflow question is a copy of the one in this forum, not the other way round.
The post looked a bit naive, but not entirely unreasonable. In the original form (naming the software package in bioinformatics) it looked like something you might have thrown at you at work (or, more likely in this instance, university research) without much help. A lot of bioscience researchers (my younger daughter being one) use R as a statistical programming language. I can well conceive them asking such a question about interfacing to C++ in this forum.
So, did the OP edit it for spam, or is somebody trigger-happy?
I do agree on your assessment. A student could easily get a "learn by fixing this" task in a biolab. The R core is not a tiny project, there are plenty of "R packages", and some of those packages contain compiled (C/C++) bits for efficiency. Not necessarily the easiest content to learn with.