Modifying Win95 master environment

[John Baird]

I've asked this before without success, but another need has arisen ...

How do I programmatically modify the master environment under Win95? I
know the WINSET util can do it, but how does it do it?

TIA, John

[Smithgall, Evan]

Take a look at this. I was looking for the same thing months back and found
this example but decided did not use it. This might work for you.

/* +++Date last modified: 28-Sep-1996 */

#include <stdio.h>
#include <dos.h>
#include <string.h>
#include <ctype.h>

#if defined(__TURBOC__) || defined(__POWERC) || defined(__ZTC__)
#if defined(__ZTC__)
#include <dos.h>
#else
#include <alloc.h>
#endif
#else /* MSC, Watcom */
#include <malloc.h>
#endif

#include "extkword.h"
#include "mk_fp.h"

struct EnvRec {
unsigned EnvSeg; /*Segment of the environment*/
unsigned EnvLen; /*Usable length of the environment*/
} EnvRec;

struct EnvRec *MasterEnv(void)
{
unsigned owner;
unsigned mcb;
unsigned eseg;
static struct EnvRec env;

env.EnvSeg = env.EnvLen = 0;
owner = * ((unsigned FAR *) MK_FP(0, (2+4*0x2e)));

/* int 0x2e points to command.com */

mcb = owner -1;

/*Mcb points to memory control block for COMMAND */

if ( (*((char FAR *) MK_FP(mcb, 0)) != 'M') &&
(*((unsigned FAR *) MK_FP(mcb, 1)) != owner) )
return (struct EnvRec *) 0;

eseg = *((unsigned FAR *) MK_FP(owner, 0x2c));

/* Read segment of environment from PSP of COMMAND} */
/* Earlier versions of DOS don't store environment segment there
*/

if ( !eseg )
{

/* Master environment is next block past COMMAND */

mcb = owner + *((unsigned FAR *) MK_FP(mcb, 3));
if ( (*((char FAR *) MK_FP(mcb, 0)) != 'M') &&
(*((unsigned FAR *) MK_FP(mcb, 1)) != owner) )
return (struct EnvRec *) 0;
eseg = mcb + 1;
}
else mcb = eseg-1;

/* Return segment and length of environment */

env.EnvSeg = eseg;
env.EnvLen = *((unsigned FAR *) MK_FP(mcb, 3)) << 4 ;
return &env;
}

/*
** Then a function to find the string to be replaced. This one'll
** return a pointer to the string, or a pointer to the first (of 2)
** NUL byte at the end of the environment.
*/

char FAR *SearchEnv( char FAR *eptr, char *search )
{
char FAR *e;
char *s;
while ( *eptr )
{
for ( s=search, e=eptr; *e && *s && (*e == *s); e++, s++ )
; /* NULL STATEMENT */
if ( !*s )
break;
while ( *eptr )
eptr++; /* position to the NUL byte */
eptr++; /* next string */
}
return eptr;
}

/*
** Now, the function to replace, add or delete. If a value is not
** given, the string is deleted.
*/

int SetEnvStr( struct EnvRec *env, char *search, char *value )
{
/* -Set environment string, returning true if successful */

char FAR *envptr;
register char FAR *p;
char *s;
int newlen;
int oldlen;
int i;

if ( !env->EnvSeg || !search )
return 0;

/* get some memory for complete environment string */

newlen = strlen(search) + sizeof((char) '\0') + strlen(value) + 2;

if ( (s = (char *) malloc( newlen)) == NULL )
return 0;
for ( i = 0; *search; search++, i++ )
s[i] = *search;
s[i++] = '=';
s[i] = '\0';
envptr = SearchEnv((char FAR *) MK_FP(env->EnvSeg, 0), s );
if ( *envptr )
{
for ( p = envptr, oldlen = 0; *p; oldlen++, p++ )
; /* can't use strlen() because of far pointer */
} /* will set p to point to terminating NUL */

if ( *value && (newlen > (int)env->EnvLen) ) /* not a deletion */
{
free( s );
return 0; /* won't fit */
}

if ( *envptr ) /* shift it down */
{
for ( ++p; (*p || *(p+1)); envptr++, p++ )
*envptr = *p;
*envptr++ = '\0';
*envptr = '\0';
}
if ( *value ) /* append it */
{
strcat(s, value);
while ( *s )
*(envptr++) = *s++;
*envptr++ = '\0';
*envptr = '\0';
}
free(s);
return 1;
}

/*
** Ok, just to show you that I tested it :
*/

main()
{
char vn[80];
char va[80];
struct EnvRec *p = MasterEnv();

puts("enter variable name:");
gets(vn);
puts("enter value:");
gets(va);
printf("SetEnvStr returned %d\n", SetEnvStr( p, strupr(vn), va) );

return 0;
}

John Baird <jo...@jrbsoftware.com> wrote in message
news:37F3D5FF...@jrbsoftware.com...

[John Baird]

Smithgall, Evan wrote:

> Take a look at this. I was looking for the same thing months back and found
> this example but decided did not use it. This might work for you.

Evan

Thanks for that. It is std DOS code for modifying the master environment. When
run under Win95 it modifies the environment of the DOS box in which the program
is running. I assume it should be possible though to convert this to 32 bit code
as it starts from the address of int 2e. I need to figure how to modify an
address created by MK_FP to a 32 bit style address. Suggestions anyone?

John