optparse VS RetroBASIC

Between -std=c99 and removing these headers, you're missing time definitions (struct timeval, gettimeofday) and option parsing definitions (struct option, getopt_long). Mingw-w64 provides all this for compatibility, but MSVC has none of these, so you'll need to write replacements. I've written embeddable, public domain implementations of getopt and something like getopt_long, in case that helps. These are how I deal with option parsing portability.

getopt_long is a GNU extension, common across unix-like systems, for parsing long options. You can find libraries for functionality as well.

When I need something more sophisticated, where long options would be nice, I reach for my own Optparse.

https://github.com/skeeto/optparse (short and long)

This is bug-free and feature complete so it never needs to be updated. When I need argument parsing in a C program, I just copy-paste that into my source and massage it into place. Sometimes I cut the fprintf() stuff, or replace the isalnum, or otherwise adapt it to fit the program's needs. The point is that it becomes wholly owned by the project using it. It's a similar story for long option parsing.

I have a (mostly archived) project that implements BASIC. Today I got the dumb idea to use the underlying machinery to make a FOCAL) interpreter. So I duplicated the original folder and in I went.

I have a very simple C console-based program based on flex/bison/c. It uses only standard libraries and has no external dependencies. It compiles on macOS using Xcode or a simple makefile, and appears to work fine on Linux using the same makefile.