Date: Thu, 30 Sep 1999 13:35:57 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
X-Sender: eliz AT is
To: Laurynas Biveinis <lauras AT softhome DOT net>
cc: djgpp-workers AT delorie DOT com
Subject: Re: Help with arg passing
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On Wed, 29 Sep 1999, Laurynas Biveinis wrote:

> > What is passed to DOS is the SFN, since 214B requires it.  What the
> > invoked program gets in its argv[0] (via !proxy), if it is a DJGPP
> > program, is the original LFN file name with its full path prepended.
> > A non-DJGPP program gets the SFN, since it has no other means of
> > getting at the command line except as passed by DOS.
> 
> If this above is true, then could you explain me what I'm doing wrong here:
[snip]
> file test.c:
> ----------
> #include <stdlib.h>
> 
> int main(void)
> {
>    system("VeryLongName.exe");
>    return 0;
> }
> ----------
> 
> When I call test, I see:
> c:/djgpp/programs/djgpp/verylong.exe
> and not
> c:/djgpp/programs/djgpp/VeryLongName.exe
> 
> What I'm doing wrong here?

You aren't doing wrong anything, it's just one of the subtleties, and
my description above was lacking a crucial detail.

The missing piece in this puzzle is that the !proxy method is used by
`system' only if the command line is longer than the DOS limit;
otherwise, the child program is invoked as non-DJGPP programs would,
with all its command-line arguments passed via the DOS call.  (The
reason for this is my own conservatism in the face of all the
subtleties that go on in system.c, dosexec.c, and c1args.c: when I did
the change that enabled long command lines in `system', I wanted to
minimize any adverse effects of some subtle misfeature that could be
lurking somewhere.)

Your test.c uses a very short command, so it doesn't get passed
through !proxy, in which case argv[0] on the child side gets set to
whatever was passed to DOS, which is the 8+3 alias.  See the function
__crt0_setup_arguments in src/libc/crt0/c1args.c, and watch the logic
that sets the variable prepend_argv0 to zero or non-zero there.

Try the modified test.c below, and you will see the long file name in
argv[0].  I think that invoking with spawnXX will also cause an LFN
variant of argv[0] to be seen by the child.

#include <stdlib.h>

int main(void)
{
   system("VeryLongName.exe"
	  " 1234567890 1234567890 1234567890 1234567890 234567890"
	  " 1234567890 1234567890 1234567890 1234567890 1234567890"
	  " 1234567890 1234567890");
   return 0;
}