Re: question on spawning DOS from C prog

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3 total messages Started by JOHN M. TROIANO Thu, 07 Jan 1993 14:05

#7499

Author: JOHN M. TROIANO
Date: Thu, 07 Jan 1993 14:05

69 lines
2313 bytes

In article <tim.36.726368023@tim.src.utah.edu>, tim@tim.src.utah.edu (Tim Ma) wr
ites:
>>Subject: Re: question on spawning DOS from C prog
>>Date: 6 Jan 93 10:50:55 GMT
>>jmt7@ns1.cc.lehigh.edu (JOHN M. TROIANO) writes:
>>
>>>For example, after spawning DOS the user would
>>>see:
>>>            <Type EXIT to return to program>      <--this would appear
>>>                                                     each time <RET> hit
>>>            C:\
>>>    Is there, perhaps, a parameter to COMMAND.COM to do this?
>
>Reply was:
>------------------------------------------------------------------------
>>In your function declare something like:
>>
>>      static char prompt[]="PROMPT=<Type EXIT to return to program>$_$_$P";
>>
>>and before the spawnl() do a
>>
>>      putenv(prompt);
>>
>>to get exactly what you want.
>>
>>Greetings,
>>Wolfgang
>>--
>>siebeck@infoac.rmi.de (Wolfgang Siebeck)
>
>Is this possible?  It was my understanding that 'spawn' called a new command
>shell so any changes in the environment would not be carried over.
>
>I've always used 'spawnl' with the 'e' suffix to set or pass on environment
>variables.
>
>Curiously,
>
>Tim Ma
>Associate Programmer
>University of Utah
>Email:  tim@src.cppa.utah.edu
>

Hi, I am the original poster of this problem: this is especially to
Tim and Wolfgang. I tried the code below (which is I think what both
of you guys are suggesting) but it does'nt work (the new prompt
string is ignored). Any ideas?     - John.

#include <stdio.h>
#include <process.h>
#include <dos.h>
#include <stdlib.h>

int main( int argc, char *argv[], char **envp )
{

printf( "\ninside main, spawning DOS\n" );
sleep( 2 );

putenv( "prompt=$_type EXIT to return to program $_$_$p$g" );

spawnlpe( P_WAIT, "command.com", NULL, envp );

printf( "\nback from spawn!\n" );

sleep( 2 );

}

Re: question on spawning DOS from C prog

#7520

Author: Chris Fortier
Date: Fri, 08 Jan 1993 00:59

51 lines
2013 bytes


In article <1993Jan7.140524.15787@ns1.cc.lehigh.edu> jmt7@ns1.cc.lehigh.edu (JOHN M. TROIANO) writes:

[ STUFF DELETED ]

   Hi, I am the original poster of this problem: this is especially to
   Tim and Wolfgang. I tried the code below (which is I think what both
   of you guys are suggesting) but it does'nt work (the new prompt
   string is ignored). Any ideas?     - John.

   #include <stdio.h>
   #include <process.h>
   #include <dos.h>
   #include <stdlib.h>

   int main( int argc, char *argv[], char **envp )
   {

   printf( "\ninside main, spawning DOS\n" );
   sleep( 2 );

   putenv( "prompt=$_type EXIT to return to program $_$_$p$g" );

   spawnlpe( P_WAIT, "command.com", NULL, envp );

   printf( "\nback from spawn!\n" );

   sleep( 2 );

   }



Sigh.  Please RTFM.  The third parameter to spawn???() is argv[], a list of
parameters to the spawned executable.  This means that argv[0] must be the
name of the executable.  I know this seems redundant, but it does have a
purpose (changing path information, passing info to the child program, etc.).

Change the spawn???() command to the following, and the program should work:

	spawnlpe(P_WAIT, "command.com", "command.com", NULL, envp);
                                ^              ^              
                                |              |        
                               path         argv[0]     


Chris Fortier
Borland C++ Run Time Library QA

cfortier@borland.com

Re: question on spawning DOS from C prog

#7561

Author: Lee Hollingworth
Date: Sat, 09 Jan 1993 10:32

49 lines
1718 bytes

jmt7@ns1.cc.lehigh.edu (JOHN M. TROIANO) writes:

>In article <tim.36.726368023@tim.src.utah.edu>, tim@tim.src.utah.edu (Tim Ma) wr
>ites:

>Hi, I am the original poster of this problem: this is especially to
>Tim and Wolfgang. I tried the code below (which is I think what both
>of you guys are suggesting) but it does'nt work (the new prompt
>string is ignored). Any ideas?     - John.

I am neither Tim nor Wolfgang, but the following *does* work!

#include <process.h>
#include <stdlib.h>
#include <stdio.h>

int shell(char *);

void main(void)
{
   static char *message = "PROMPT=Type EXIT to return to program $_$P$G ";

   if (shell(message) == -1) {
      fprintf(stderr, "Error: cannot shell to DOS\n");
   }
}

/***
 * function: shell
 * purpose:  shell out to DOS operating system.
 * passed:   prompt -- prompt to be displayed in DOS environment.
 * returns:  -1 -- error occured
 *            ? -- the child process's exit status
 ***/
int shell(char *prompt)
{
   char *comspec = getenv("COMSPEC");

   if (!comspec) {
      return -1;
   }
   if (putenv(prompt)) {
      return -1;
   }
   return spawnl(P_WAIT, comspec, NULL);
}

Lee Hollingworth
s1110238@giaeb.cc.monash.edu.au

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