Porting csol to DOS for no reason

Thu, 19 Apr 2018 19:4:0 +0200

csol running in DOS 6.22 on an i486 Toshiba laptop from the mid-'90s.

I'm not sure how the thought entered my mind, but I was suddenly curious about how easy it would be to get a somewhat simple ncurses application like csol to run on DOS. Aside from ncurses, I knew csol didn't really have any dependencies other than a C compiler, so I searched for “DOS curses” and PDCurses (Public Domain Curses) showed up.

Helpfully, the PDCurses github repository contains a list of C compilers for DOS. At first I tried to get DJGPP up and running in DOSBox, but eventually ended up using Open Watcom instead because the installation was simpler. After compiling PDCurses my new DOS development environment was ready. To compile csol with Open Watcom and PDCurses I had to make a number of changes to the source:

From C99 to ANSI C: The first step was to remove the use of C99 features from the source code. One such feature is the ability to declare variable anywhere in a block, whereas in ANSI C all declarations must be at the top of the block. This was rather easy to fix by running each source file through gcc -c -ansi -pedantic which helpfully lists all incompatibilities.

From ncurses to pdcurses: Rather unexpectedly it was enough to just include curses.h instead of ncurses.h and change a single occurrence of getmouse(&mouse) to nc_getmouse(&mouse).

From POSIX to DOS: The csol configuration file format has support for including entire directories (e.g. the games and themes directories). Unfortunately standard C doesn't have any concept of “directories” so in order to get the contents of a directory I had used the dirent.h header which is part of the C POSIX library. No such header is provided by Open Watcom, but I was able to recreate the functionality using the functions _dos_findfirst() and _dos_findnext() which are part of the dos.h header.

Similarly I had used getopt_long() from getopt.h (a GNU header) to parse command line options. I replaced this with getopt() from unistd.h (which Open Watcom does include). Unfortunately this means that long options are not currently supported.

From Unicode to Code page 437: The default csol theme uses several Unicode characters to draw cards and suits. Since DOS doesn't support Unicode I created a new default theme based on Code page 437 which happens to include the exact same characters I was using in the Unicode theme.

The modified source code is available on github. I've also uploaded a zip-file containing the compiled EXE and configuration files. It works in DOSBox, and I was also able to run it directly from a 3.5″ floppy on my Toshiba T2130CS with a 486. It should also work on older 386 and 286 machines.