Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!texbell!texsun!letni!sneaky!merch!spudge!thorp
From: thorp@spudge.UUCP (Don Thorp)
Newsgroups: comp.sys.ibm.pc
Subject: Re: MS-DOS Environment Variables
Message-ID: <6551@spudge.UUCP>
Date: 21 Nov 89 15:27:22 GMT
References: <5679@wpi.wpi.edu> <1989Nov20.212803.5326@uwasa.fi>
Reply-To: thorp@spudge.UUCP (Don Thorp)
Organization: Friends of Guru Bob
Lines: 88

The following code will set an environment variable in the highest 
environment.  I compiled it with tasm and zortech cpp.  But there should
be no changes required for MSC or TurboC.  The transient portion of
command.com will be loaded.  If there is not enough memory to load 
command.com, your system will crash.  That is one of the side effects of 
using interrupt 2Eh.

Don Thorp
USENET ...!texbell!letni!rwsys!spudge!thorp

<------------------------------Cut Here----------------------------------->
/**********************************************************************
 * setenv.h
 *
 **********************************************************************/

#if !defined(__SETENV_H__)

#define __SETENV_H__

#if defined(__cplusplus)
extern "C" {
#endif

void int2e(char *cmd);
void setenv(const char *p);

#if defined(__cplusplus)
}
#endif

#endif
<------------------------------Cut Here----------------------------------->
/*************************************************************************
 * setenv.c - Set the root environment
 *
 ************************************************************************/

#include <stdlib.h>
#include <string.h>

#include "setenv.h"

void setenv(const char *p) {

  char *cmd = malloc(strlen(p) + 3);

  cmd[0]=strlen(p);
  strcpy(cmd+1,p);
  strcat(cmd+1,"\r");

  int2e(cmd);

  free(cmd);
}
<------------------------------Cut Here----------------------------------->
;  Interrupt 2Eh Call for C  int2e.asm
;
;  void _int2e(char *cmd)
;
                Public _int2e
_TEXT           Segment Byte Public 'CODE'
                Assume CS:_TEXT

Stack           dw      ?,?

_INT2E          proc    near
                push    bp
                mov     bp,sp
                push    si                      ;Save registers
                push    di
                push    ds
                mov     cs:[Stack], sp          ;Save the stack pointer
                mov     cs:[Stack+2], ss
                mov     si, ss:[bp+4]           ;Get parameter

                int     2eh                     ;do interrupt

                mov     ss, cs:[Stack + 2]      ;restore stack
                mov     sp, cs:[Stack]
                pop     ds
                pop     di
                pop     si
                pop     bp
                ret
_INT2E          endp
_TEXT           ends
                end