This code works fine with an array size of 100,000 when I try to increase
the size to 1,000,000 it crashes. After debugging it indicates a stack
overflow has occured. Why is this happening? I have 64 meg of memory.P2 300
mhz win95.The compiler is VC++ 5.0.

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

int compare_long(long *a, long *b)
 {
  if (*a < *b)
   return(-1);
  else if (*a == *b)
   return(0);
  else
   return(1);
 }

void main(void)
 {
   long long_values[100000];   /* when changed to 1000000 it crashes */

 long elements = 100000, i;     /* when changed to 1000000 it crashes */
 printf("Here we go \n");
 getchar();

 for (i = 0; i < elements; i++)
  long_values[i] = i;

 printf("done initializing array\n");
 getchar();

 qsort(long_values, elements, sizeof(long),
      (int (*) (const void *, const void *)) compare_long);

 for (i = 0; i < elements; i++)
     printf("%d ", long_values[i]);

 putchar('\n');

 }

--

Maybe something in the WIN32 architecture needs to be done differenetly,
since this works flawlessly (printing all 1M integers to my screen).
Maybe you need a flag for your compiler to make sure it is ANSI compliant,
and doesn't try any wierd optimizations?

B.

--

   Brian P. Hampson                  ASL Analytical Service Laboratories Ltd
   System Administrator,             Vancouver, BC (604)253-4188
      ----------------- http://www.ASL.CA/ ----------------------------  

I'm not speaking for the company <- They made me say that.
--

: : hi,
: :
: : This code works fine with an array size of 100,000 when I try to increase
: : the size to 1,000,000 it crashes. After debugging it indicates a stack
: : overflow has occured. Why is this happening? I have 64 meg of memory.P2 300
: : mhz win95.The compiler is VC++ 5.0.

: Maybe something in the WIN32 architecture needs to be done differenetly,

        Like, diddling a registry entry perhaps (No idea, but _everything_
seems to be in the registry... :-)

: since this works flawlessly (printing all 1M integers to my screen).

        Then just keep bumping the array size up until it does croak.
4 and 8 meg stack limits are pretty common on a lot of OSes.

        ANSI/ISO C does not, AFAIK, require an implementation to
allow truly arbitrary sized arrays. Most OSes have some notion of
"a reasonable stack", among other reasons to allow them to detect
processes with runaway recursion. _Usually_, there is a way to
say "Trust me, I know what I'm doing" to such OSes. Of course, one
could make the argument that someone who declares such an array
locally, and does not pretty much immediately turn to the "How
to increase process stack size" section of the manual in case of
errors, does _not_ truly know what he's doing... :-)

                                                Mike

--

One hint, a decent qsort() implementation requires a stack
that is at worst proportional to lg(elements).

Ta',
Juergen

--
\ Real name     : Jrgen Heinzl                 \       no flames      /

--

Francis Glassborow      Journal Editor, Association of C & C++ Users
64 Southfield Rd
Oxford OX4 1PA          +44(0)1865 246490
All opinions are mine and do not represent those of any organisation
--

Secondly sizeof(long) could be anything and on a system with 8-bit chars
and 64 bit longs your array of 1000000 will require just under 8Mbytes
which is a hell of a lot of stack space (and would hardly make your
program popular on a multi-tasking system.

Based on the error message, this array is clearly too big to place on your
stack, on your system.

Do it this way:

long *long_values = malloc(100000 * sizeof long);

--

Paul Lutus
www.arachnoid.com

<snip>

--

   long *long_values = malloc(100000 * sizeof long);

Parentheses are required for a type name:
   long *long_values = malloc(100000 * sizeof (long));
or
   long *long_values = malloc(100000 * sizeof *long_values);

--
"You know, they probably have special dorms for people like us."
--American Pie
--

--

Paul Lutus
www.arachnoid.com

static long long_values[1000000];

  Another possibility is to use a larger or expandable stack, look for
linker options for doing that.

  Michael

--
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