_heapset

Checks heaps for minimal consistency and sets the free entries to a specified value.

int _heapset( unsigned int fill );

For additional compatibility information, see Compatibility in the Introduction.

Libraries

Return Value

_heapset returns one of the following integer manifest constants defined in MALLOC.H:

_HEAPBADBEGIN

Initial header information invalid or not found

_HEAPBADNODE

Heap damaged or bad node found

_HEAPEMPTY

Heap not initialized

_HEAPOK

Heap appears to be consistent

In addition, if an error occurs, _heapset sets errno to ENOSYS.

Parameter

fill

Fill character

Remarks

The _heapset function shows free memory locations or nodes that have been unintentionally overwritten.

_heapset checks for minimal consistency on the heap, then sets each byte of the heap’s free entries to the fill value. This known value shows which memory locations of the heap contain free nodes and which contain data that were unintentionally written to freed memory.

Note In Visual C++ Version 4.0, the underlying heap structure was moved to the C run-time libraries to support the new debugging features. As a result, the only Win32 platform that is supported by _heapset is Windows NT. The function returns _HEAPOK and sets errno to ENOSYS, when it is called by any other Win32 platform.

Example

/* HEAPSET.C: This program checks the heap and
 * fills in free entries with the character 'Z'.
 */

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

void main( void )
{
   int heapstatus;
   char *buffer;

   if( (buffer = malloc( 1 )) == NULL ) /* Make sure heap is */
      exit( 0 );                        /*    initialized    */  
   heapstatus = _heapset( 'Z' );        /* Fill in free entries */
   switch( heapstatus )
   {
   case _HEAPOK:
      printf( "OK - heap is fine\n" );
      break;
   case _HEAPEMPTY:
      printf( "OK - heap is empty\n" );
      break;
   case _HEAPBADBEGIN:
      printf( "ERROR - bad start of heap\n" );
      break;
   case _HEAPBADNODE:
      printf( "ERROR - bad node in heap\n" );
      break;
   }
   free( buffer );
}

Output

OK - heap is fine

Memory Allocation Routines

See Also   _heapadd, _heapchk, _heapmin, _heapwalk