open-watcom-v2 VS rust_dos

https://github.com/open-watcom/open-watcom-v2

In terms of ISO-complianceness, perhaps don't expect much. It basically C89 (the C99 support is still incomplete), and for C++... most likely not even C++98 - compliant.

> You will also want to start with a 16-bit C compiler like Borland Turbo C or Microsoft C

The parent post mentioned they're going to use OpenWatcom which is an actively developed[0] C and C++ compiler that targets 16bit DOS (among others).

[0] https://github.com/open-watcom/open-watcom-v2

Despite the lack of feature support, the compiler is still updated to this day, and still does support DOS, Windows, Linux, and OS/2, so it's modern in the sense of maintenance, just not really standards support. If you got further questions, I can send you the Discord link. They are pretty friendly.

My advice is, when you feel you need that challenge, install DOSBox or DOSBox-X and Open Watcom C/C++, DJGPP, or gcc-ia16 and do some retro-programming. You'll also get the fun of being able to do low-level hardware twiddling and rely on DOS being so simple that it's effectively an RTOS.

If you want to build under Linux, I would recommend you look at Open Watcom. It's the best open source 16-bit x86 C compiler, IMHO.

I have recently found out that Watcom C still exists. And not just exists, but there are plenty of commits.

I should note, that OpenWatcom 2.0[1] is far better for supporting more recent C and C++ code, modern hosts and tooling, but still able to compile into 16 bit code. It is also actively maintained. Instead of MASM I recommend JWasm[2] + Jwlink[3]. Back in time I did a fork[4] of JWasm that has cleaner build system (CMake).

[1] https://github.com/open-watcom/open-watcom-v2

[2] https://github.com/Baron-von-Riedesel/JWasm

[3] https://github.com/JWasm/JWlink

[4] https://github.com/JWasm/JWasm

If you want to run this in DOS: the code under src/should actually compile with this OpenWatcom fork via the -za99 flag. MiniFB however will not compile. You'd have to palettize the output pixel buffer to 256 colors and then blit it to 0xa000if you fancy that.

GCC, clang or maybe watcom? You wouldn't find it there (before invention of AGI, but that would be entirely different can of worms).

You do not need segment registers much if you stick to the tiny model. Here is someone compiling Rust to a 16-bit DOS COM executable:

https://github.com/o8vm/rust_dos

Not sure what the approach would be for them to expand that to support segments.

In DJGPP there are macros to allow your protected mode application access physical real-mode addresses (like when you want to write to video RAM). I don't know if IA-16 also does something like that, or if they added far/near keywords to the language like old 16-bit C compilers did (at least the ones I used).

Free Pascal has helper-functions to work with segment+offset pointer pairs, also without having to modify the language itself. I think that would work well enough in C, but I guess the old method of adding non-standard keywords was seen as slightly more convenient.

Demo: https://github.com/o8vm/rust_dos

It is probably possible for almost any old platform with some cross-compilation magic, but not anything that will be officially supported as the compiler-makers focus on modern systems. There is for instance an unofficial 16-bit DOS backend for GCC and at least one or two projects to compile Rust to DOS-executables (that I assume use Clang?) (in addition to 32-bit DJGPP(gcc) for MSDOS that I linked to above). Probably are similar projects to target 68k somewhere?