ID Number: Q51742
5.10 6.00 6.00ax 7.00
MS-DOS
Summary:
SYMPTOMS
In Microsoft C versions 5.1, 6.0, 6.0a, 6.0ax, and C/C++ version
7.0, using spawn() to create a child process and then attempting to
increase the environment space of the child (by adding a new
environment variable or expanding an existing environment
variable), results in the following error:
Out of Environment Space
This problem does NOT happen under OS/2.
RESOLUTION
To work around this problem, set up a dummy environment variable
that is large enough to hold the new environment variable you plan
to use in the spawned process. When the child process is called,
you can then set the dummy variable to null (with a "set dummy="),
then you can set your processes environment variable. Please note
that this will change the dummy environment variable for the child
only, not the parent process.
More Information:
The following program(s) illustrates this behavior:
Sample Code
-----------
/*-----------------------------------------------------------------*/
/*-----------------------------------------------------------------*/
parent.c This will call the child process (child) with the spawnlp
function.
/*-----------------------------------------------------------------*/
#include <stdio.h>
#include <process.h>
void main (void);
void main (void)
{
printf ("In the parent process\n");
spawnlp (P_WAIT, "child.exe", "child", NULL);
printf ("\nAnd back to the parent process.\n");
}
/*-----------------------------------------------------------------*/
child.c Called by parent.c, uses the system function to call a batch
file (BATCH.BAT) to attempt to set a new environment variable.
/*-----------------------------------------------------------------*/
#include <stdio.h>
#include <process.h>
#include <conio.h>
#include <errno.h>
void main (void);
void main (void)
{
printf ("At child process...\n");
system ("batch.bat");
getch ();
}
/*-----------------------------------------------------------------*/
BATCH.BAT The batch file, which is called by the child process
(CHILD.EXE). It just shows the environment variables,
attempts to set another environment variable, then shows
the environment variables one more time.
/*-----------------------------------------------------------------*/
set
set blah=thisisatestonlyatestsoitdoesnotreallymatter
set
/*-----------------------------------------------------------------*/
Parent will spawn child, which in turn spawns (through system)
BATCH.BAT. The idea is to show that when BATCH.BAT is called, an "Out
of Environment Space" error will be given. Yet, if BATCH.BAT is run
from MS-DOS, no such error is issued.
Under MS-DOS, the child receives only enough space to hold the current
environment variables, while under OS/2, the segment that holds the
environment can usually be expanded.
Additional reference words: 5.10 6.00 6.00a 6.00ax 7.00