DOS ain't dead

trip report: Tiny C Compiler 0.9.27 (Miscellaneous)

posted by bretjohn  , Rio Rancho, NM, 06.02.2026, 01:59

> Not sure the exact limit. Maybe you mean minus the length byte and actual
> ending CR.

That's exactly what I meant.

> I know the DOS4GW extender couldn't handle longer than 126 or
> so. I had thought I read %CMDLINE% was only used when 7Fh or 80h
> (Borland??) length was found.

I don't think you can depend on that in all cases (basically, an illegal value in the length byte). E.g., I know some programs if they perform an EXEC call don't set up the command-tail portion of the call correctly (in particular, they don't always set the size byte correctly). So if your program gets EXEC'd from another program you can't always depend on the size byte being correct (that's part of the reason I ignore it except to detect the potential presence of %CMDLINE%). In my programs I test for the length byte being >=7Eh, not exactly 7Eh, before looking for %CMDLINE%. But I also don't assume that just because it's a big value doesn't mean I'll necessarily find %CMDLINE%. And as I stated earlier, the user (or another program) can set %CMDLINE% so just because it exists doesn't mean it's associated with the command-tail.

If you're writing in a high-level language you usually depend on the compiler to handle all those details for you, and a lot of them (especially older ones) don't do it correctly with modern versions of DOS. At least in some cases you can bypass what the compiler does and look at the PSP and environment space yourself, but that sort of defeats the purpose of using a high-level language (it's supposed to handle those kinds of details automatically). When MS (or somebody else) changes the rules you can end up with messy crashes and bugs.

Complete thread:

• trip report: Tiny C Compiler 0.9.27 - bencollver, 04.02.2026, 17:02 (Miscellaneous)
  • trip report: Tiny C Compiler 0.9.27 - tkchia, 04.02.2026, 17:55
    • trip report: Tiny C Compiler 0.9.27 - bencollver, 04.02.2026, 18:48
      • trip report: Tiny C Compiler 0.9.27 - Japheth, 04.02.2026, 21:12
        • trip report: Tiny C Compiler 0.9.27 - bencollver, 04.02.2026, 21:44
        • trip report: Tiny C Compiler 0.9.27 - bretjohn, 05.02.2026, 22:24
          • trip report: Tiny C Compiler 0.9.27 - Rugxulo, 05.02.2026, 23:09
            • trip report: Tiny C Compiler 0.9.27 - bretjohn, 06.02.2026, 01:59
      • trip report: Tiny C Compiler 0.9.27 - bencollver, 04.02.2026, 21:38
        • trip report: Tiny C Compiler 0.9.27 - tkchia, 05.02.2026, 16:44
          • trip report: Tiny C Compiler 0.9.27 - bencollver, 05.02.2026, 18:34
            • trip report: Tiny C Compiler 0.9.27 - bencollver, 05.02.2026, 22:22
              • trip report: Tiny C Compiler 0.9.27 - tkchia, 05.02.2026, 23:13
              • trip report: Tiny C Compiler 0.9.27 - Rugxulo, 05.02.2026, 23:16
              • trip report: Tiny C Compiler 0.9.27 - tkchia, 05.02.2026, 23:18
              • trip report: Tiny C Compiler 0.9.27 - tkchia, 06.02.2026, 23:45
  • trip report: Tiny C Compiler 0.9.27 - bencollver, 11.02.2026, 00:44
    • trip report: Tiny C Compiler 0.9.27 - Rugxulo, 11.02.2026, 01:42
      • trip report: Tiny C Compiler 0.9.27 - bencollver, 11.02.2026, 02:06