Cogs and Levers A blog full of technical stuff

32bit DOS Development with Open Watcom

04 Oct 2015

The Watcom Compiler is an open source C & C++ compiler that has a very successful history when it was discovered that the DOOM developers were using it. That was a very long time ago, but that shouldn’t stop us having a go!

Installation

I’ve grabbed the dos bundle from the Open Watcom FTP site and installed it into DosBox. The only problem with this setup, it that I much prefer to use a text editor that’s outside of the DOS environment (like emacs/sublime, etc.) DosBox sometimes has a bit of difficulty picking up file system changes that have been mounted in.

Shift + Ctrl + F4 (documented as just Ctrl + F4) forces DosBox to refresh its mounts.

Very handy.

The Tools

There are a bucket of binaries that are bundled with the installation.

Utility Description
wasm.exe Assembler
whelp.exe Help Command Line
wmake.exe Make utility
wcl386.exe Compile and Link
wpp386.exe Optimizing compiler
wcc386.exe Optimizing compiler
wd.exe Debugger
wlib.exe Library manager
wlink.exe Linker
dos32a.exe DOS32A extender
wdis.exe Disassembler

For convenience, we’ll use wcl386.exe as this will perform the compilation and linking step in one for us.

Compiling and Linking

Prior to compilation and linking, things will go a lot smoother if you’ve prepared your environment variables correctly.

SET PATH C:\WATCOM\BINW;%PATH%;
SET INCLUDE=C:\WATCOM\H;
SET WATCOM=C:\WATCOM
SET EDPATH=C:\WATCOM\EDDAT
SET WIPFC=C:\WATCOM\WIPFC

Open up your favorite editor and create a hello world application, called hello.cpp.

#include <stdio.h>

int main(int argc, char *argv[]) {
  printf("Hello, world!\n");
  return 0;
}

Now build it with wcl386.exe:

C:\SRC> wcl386 hello.cpp
Open Watcom C/C++32 Compile and Link Utility Version 1.9
Portions Copyright (c) 1988-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.
See http://www.openwatcom.org/ for details.
  wpp386 HELLO.CPP 
DOS/4GW Protected Mode Run-time  Version 1.97
Copyright (c) Rational Systems, Inc. 1990-1994 
Open Watcom C++32 Optimizing Compiler Version 1.9
Portions Copyright (c) 1989-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.
See http://www.openwatcom.org/ for details.
HELLO.CPP: 7 lines, included 1160, no warnings, no errors
  wlink @__wcl__.lnk
DOS/4GW Protected Mode Run-time  Version 1.97
Copyright (c) Rational Systems, Inc. 1990-1994 
Open Watcom Linker Version 1.9
Portions Copyright (c) 1985-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.
See http://www.openwatcom.org/ for details.
loading object files
searching libraries
creating a DOS/4G executable

We can now run our application:

C:\SRC> hello.exe
DOS/4GW Protected Mode Run-time  Version 1.97
Copyright (c) Rational Systems, Inc. 1990-1994 
Hello, world

What is DOS/4GW?

To a lot of us, the DOS/4GW is a very familiar banner that we saw when we’d fire up one of our favorite games. But, what is it?

Wikipedia’s article defines its role pretty well:

DOS/4G is a 32-bit DOS extender developed by Rational Systems (now Tenberry Software). It allows DOS programs to eliminate the 640 KB conventional memory limit by addressing up to 64 MB of extended memory on Intel 80386 and above machines.

It’s the resident binary that gets packaged with your compiled application that facilitates access to the computers’ full array of resources. Without it, you’d be stuck with what DOS provides you by default.

Conclusion

Well, it’s always nice to go over this old stuff. In my next posts, I’ll cover inline assembly and mode 13/x to get a head start on writing DOS games in the 90’s!

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