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#include <stdio.h>
#include <dos.h>
#include <string.h>
#include <ctype.h>
#ifdef __TURBOC__
#include <alloc.h>
#define FAR far
#else
#include <stdlib.h>
#define FAR _far
#endif
#if !defined(MK_FP)
#define MK_FP(seg,off) ((void FAR *)(((long)(seg) << 16)|(unsigned)(off)))
#endif
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 :
*/
void main(void)
{
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) );
}
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