Wrapping C code is best done in two phases: one that expresses the C ABI in Nim terms - pretty much, this is what a header file does in C - you simply replace your .h file with a .nim file and change the syntax, adding appropriate Nim annotations like bycopy and so on. After this stage, the C header file is no longer needed, but should correspond 1:1 to the Nim file.
This part can often be automated to 80:ish% - the rest needs manual overrides for the vast majority of C headers. In my experience, the best tool out there for this is Nimterop - we use it on sqlite for example: <https://github.com/arnetheduck/nim-sqlite3-abi> . I find nimterop to work better mainly because it has a much better C parser than c2nim, while it still knows about Nim quirks. The best feature it has it that it outputs a Nim file that you can further fine-tune. The next stage of writing a wrapper is to create an interface that is pleasant to use from Nim - depending on the C library, this will be easy or hard, but above all, without this stage, you'll be writing C code effectively - this wrapper cannot be generated at all, but is almost equally important. Automated solutions are nice at first look because they work for "hello world" type of code. Anyone using one should expect however that the wrapper will need further work as Nim is not a superset of C. The final point is that just like you might accidentally mismatch C headers and the compiled libraries they reference, the same thing happens with Nim files - here, it's usually good to ensure that each version of the C library has its own Nim representation - currently, the nim standard library and community is fairly lax on this point which again makes simple cases simple - unfortunately it also makes hard cases nearly-impossible to figure out (ABI mismatches are among the most difficult bugs to reason about). This is where the separate ABI description comes in - if you have one of these for each version of the C library customized for that version in particular (including all field alignments and object sizes correct), the rest will usually work.
