Subj : heapchecknode
To   : borland.public.cpp.borlandcpp
From : Tom
Date : Sun Jul 04 2004 03:34 pm

Hello,

In writting a program I created a wrapper to surround malloc/free for the
debug versions, and I noticed borland's heapchecknode et al functions. So I
used them, and they have saved me time debugging certain problems. However,
I was doing some stuff involving large allocations and have come across a
problem, which is best described by the folowing program:


#include <malloc.h>
#include <alloc.h>
#include <mem.h>
#include <stdio.h>
#include <conio.h>

void testSize(int size)
{
 void * tmp = malloc(size);
 printf("(%i) ",(int)tmp);
 int ret = heapchecknode(tmp);
 switch (ret)
 {
  case _USEDENTRY: printf("used entry (ok)\n"); break;
  case _HEAPCORRUPT: printf("heap corrupt\n"); break;
  case _BADNODE: printf("bad node\n"); break;
  case _BADVALUE: printf("bad value\n"); break;
  case _HEAPBADBEGIN: printf("heap bad begin\n"); break;
  case _HEAPBADNODE: printf("heap bad node\n"); break;
  case _HEAPBADPTR: printf("heap bad ptr\n"); break;
 }
 free(tmp);
}

int main()
{
 for (int i=1022;i<1026;i++)
 {
  printf("%i: ",i);
  testSize(i*1024);
 }

 getch();
 return 0;
}

I compiled it with the free BCC 5.5 compiler, using the simplest way
possible: 'bcc32 main.cpp'
The output is as follows:

1022: (8661496) used entry (ok)
1023: (8661496) used entry (ok)
1024: (12845060) bad node
1025: (12845060) bad node


In other words, whilst these functions work fine for blocks under 1 meg,
when equal in size or bigger than that they just don't appear to work.
Anyone know why this is?

Thanks for any help,
Tom

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