_heapset - Validate and Set Default Heap

Syntax

#include <malloc.h>
int _heapset(unsigned int fill);

heapset checks the default storage heap for minimal consistency by checking all allocated and freed objects on the heap (similar to _heapchk). It then sets each byte of the heap's free objects to the value of fill.
Using _heapset can help you locate problems where your program continues to use a freed pointer to an object. After you set the free heap to a specific value, when your program tries to interpret the set values in the freed object as data, unexpected results occur, indicating a problem.
A heap-specific version of this function, _uheapset, is also available.
Note: Using the _heapchk, _heapset, and _heap_walk functions (and their heap-specific equivalents) may add overhead to each object allocated from the heap.

heapset returns one of the following values, defined in <malloc.h>:
HEAPBADBEGIN
_HEAPBADNODE
_HEAPEMPTY
_HEAPOK

This example allocates and frees memory, then uses _heapset to set the free heap to X. It checks the return code from _heapset to ensure the heap is still valid.

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

int main (void)
{
   char  *ptr;
   int   rc;

   if (NULL == (ptr = malloc(10))) {
      puts("Could not allocate memory block.");
      exit(EXIT_FAILURE);
   }
   memset(ptr,'A',5);
   free(ptr);

   if (_HEAPOK != (rc = _heapset('X'))) {
      switch(rc) {
         case _HEAPEMPTY:
            puts("The heap has not been initialized.");
            break;
         case _HEAPBADNODE:
            puts("A memory node is corrupted or the heap is damaged.");
            break;
         case _HEAPBADBEGIN:
            puts("The heap specified is not valid.");
            break;
      }
      exit(rc);
   }
   return 0;
}

Managing Memory" in the VisualAge C++ Programming Guide
heapchk
heapmin
heap_walk
uheapset

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