getopt VS optparse

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.

The option parser is crude and doesn't follow conventions. Particularly the lack of -- support (disables option parsing) would make it impossible to use safely in scripts. If you don't want to use the system or toolchain-provided getopt, here's a public domain, embeddable implementation: getopt.h

On unix-like systems there's a getopt function for parsing short options. Mingw-w64 has one as well, to cover Windows programs. If I care about portability, I just embed my own so it not only works everywhere, it behave the same everywhere, too.

https://github.com/skeeto/getopt/blob/master/getopt.h (short)

Not only the GNU, you have an example in this thread where someone suggested to use or roll something similar to https://github.com/skeeto/getopt/blob/master/getopt.h, which, surprise, depends on strchr, a function that solves a much trivial problem than POSIX getopt, to begin with.

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.