X-Authentication-Warning: delorie.com: mail set sender to djgpp-bounces using -f
From: Georg <dosusb AT googlemail DOT com>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: argv[0]
Date: Sun, 4 Dec 2011 09:26:14 -0800 (PST)
Organization: http://groups.google.com
Lines: 84
Message-ID: <dca6ea34-7cf2-4abe-afc3-8a1122602ed9@y12g2000vba.googlegroups.com>
References: <16b04d29-8317-4c7f-929c-1a22a328fa32 AT p9g2000vbb DOT googlegroups DOT com>
 <jaueod$2t8$1 AT speranza DOT aioe DOT org> <9bf257a7-a0f8-43ba-a65f-36c6027f68cb AT r28g2000yqj DOT googlegroups DOT com>
 <jb1ejh$hm8$1 AT speranza DOT aioe DOT org> <cc43d375-8e59-425d-a32e-b4ca200ae5cc AT 4g2000yqu DOT googlegroups DOT com>
 <jbeegg$qp2$1 AT speranza DOT aioe DOT org> <dca06357-dc1d-4ede-aa9e-510e15e499b5 AT z17g2000vbe DOT googlegroups DOT com>
NNTP-Posting-Host: 92.250.191.164
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
X-Trace: posting.google.com 1323019575 28530 127.0.0.1 (4 Dec 2011 17:26:15 GMT)
X-Complaints-To: groups-abuse AT google DOT com
NNTP-Posting-Date: Sun, 4 Dec 2011 17:26:15 +0000 (UTC)
Complaints-To: groups-abuse AT google DOT com
Injection-Info: y12g2000vba.googlegroups.com; posting-host=92.250.191.164; posting-account=v5xbdQoAAAAOGc9Ccc-kLZyobvPlN3Qr
User-Agent: G2/1.0
X-HTTP-Via: 1.1 TAS-4-1.man-a
X-Google-Web-Client: true
X-Google-Header-Order: UALSERCVNKH
X-HTTP-UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; de; rv:1.9.1.4)
 Gecko/20091016 Firefox/3.5.4,gzip(gfe)
Bytes: 4177
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

I finally found a way to retrieve the absolute path to the current
program. It seems that the pointer to the environment in the PSP when
using DJGPP is wrong for whatever reason. There is a KB16 program
which has the correct pointer to the environment I am looking for in
its PSP though.

So I walked through the MCB chain to find the environment block in
there. There are two entries in there with the same PSP, one is the
environment block, the other is the program code. The latter has the
PSP right after the MCB so if that is not the case you have found the
environment block. The absolute path is then located behind the size
given in the MCB of the environment block. Here is my code:

#include <stdio.h>
#include <sys/movedata.h>
#include <dpmi.h>
#include <go32.h>

main(int argc,char **argv)
{
unsigned int es,peekword,blocksize,pspseg,environment;
unsigned short mcbid=0x4d;
unsigned long the_psp = 0;
static unsigned mcbseg; //first mcb
unsigned mcbs;
char* buff[256];
__dpmi_regs regs;

   regs.x.ax = 0x5200;        /* AH = 52h, AL = 00h  */
   __dpmi_int (0x21, &regs);  /* call DOS  */
   if (regs.x.flags & 1)      /* is carry flag set?  */
   {;}  /* The call failed*/
   else
   {
	es = regs.x.es;
	es <<= 4;
	es += regs.x.bx;
	_dosmemgetw(es-2, 1, &mcbseg);
	mcbseg <<= 4;
   }
    the_psp = _go32_info_block.linear_address_of_original_psp;

    while (mcbid==0x4d){
	mcbs=mcbseg;
		printf("\nMCB:%X \t",mcbs);
    _dosmemgetb(mcbs,1,&mcbid);
		printf("%c ",mcbid);
	_dosmemgetw(mcbs+1,1,&pspseg);
		printf("PSP:%X \t",pspseg);
	environment=pspseg<<4;
	environment += 0x2C;
	_dosmemgetw(mcbs+3,1,&blocksize);
		printf("Blocksize:%X \t",blocksize);
	if ((mcbseg+16)==pspseg*16){ //is it a program code mcb?
		_dosmemgetw(environment,1,&peekword);
		printf("ENV:%X ",peekword); //only print if program code
		dosmemget(mcbs+8,30,&buff);
		printf(" Program:%s",buff);
	}
	if (pspseg*16==the_psp) { //found the right PSP?
		//not the code but the environment block?
		if ((mcbseg+16)!=the_psp){
			dosmemget(mcbs+blocksize*16-18,30,&buff);
			printf("Path:%s",buff);
		}
	}
	//retrieve next mcb
	_dosmemgetw(mcbs+3,1,&peekword);
	peekword <<=4;
	mcbseg += peekword+0x10;
	}
return 0;
}

I should have used a different variable name instead of mcbseg but I
leave it now as it is.

Rayer may have pointed out correctly that this is all too complicated
and could be replaced by reading the value in argv[0]. But I observed
that when I start my code with "redir" argv[0] will not return the
full path. Plus DJ Delorie's post made me uncertain whether I should
use argv[0].

Georg