ID Number: Q58779
5.00 5.10 6.00 6.00a 6.00ax
MS-DOS
buglist5.10 buglist6.00 buglist6.00a buglist6.00ax buglist7.00
Summary:
SYMPTOMS
In Microsoft C versions 5.1, 6.0, 6.0a, 6.0ax, and C/C++ version 7.0,
if you have increased the maximum number of file handles and buffers
available to the system by changing the _file.c and crt0dat.asm
startup source files as outlined in the README.DOC file, and then
write a program that does multiple execs, your machine may halt under
MS-DOS.
CAUSE
There is a known incompatibility between changing the startup
source code for the optimizing C compilers and exec'ing multiple
child processes.
STATUS
Microsoft has confirmed this to be a problem in C versions 5.0,
5.1, 6.0, 6.0a, 6.0ax, and C/C++ version 7.0. We are researching this
problem and will post new information here as it becomes available.
More Information:
The sample code below demonstrates this problem. If you make a copy of
this program and call it CHILD.C, and change all references in the
CHILD.C program from child to parent, you will have a loop of exec's
set up. You can exec the child once, then your machine either hangs on
the call to exec() the first program again or as the second program is
finishing execution.
Sample Code
-----------
#define FILES_OPEN 30
#include <stdio.h>
#include <conio.h>
#include <process.h>
#include <errno.h>
#include <string.h>
void main ( void )
{
short numfiles, returnval;
FILE *FilePointer;
char fname[80];
for ( numfiles = 0; numfiles < FILES_OPEN; numfiles ++ )
{
sprintf ( fname, "file%2d.dat", numfiles ) ;
printf ( "Opening file #%2d :%s\n", numfiles, fname ) ;
if ( ( FilePointer = fopen ( fname, "a+" ) ) == NULL )
{
printf ( "fopen failed on file #%2d", numfiles ) ;
exit ( -2 ) ;
}
}
printf ( " Press <esc> to quit, other to continue exec'ing child: \n" ) ;
if ( ( returnval = getche() ) == 27 )
{
printf ( "Quitting...\n" ) ;
exit ( 1 ) ;
}
if ( ( returnval = execlp ( "child.exe", "child.exe", NULL )) == -1 )
{
printf ( "Error exec'ing child; ERRNO: %d\n", errno ) ;
}
}
Additional reference words: 5.10 6.00 6.00a 6.00ax 7.00