`_heapset`

Article
10/26/2022

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

Important

This function is obsolete. Beginning in Visual Studio 2015, it is not available in the CRT.

Syntax

int _heapset(
   unsigned int fill
);

Parameters

fill
Fill character.

Return value

_heapset returns one of the following integer manifest constants defined in Malloc.h.

Value	Description
`_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.

Remarks

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

_heapset checks for minimal consistency on the heap and 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. If the operating system doesn't support _heapset(for example, Windows 98), the function returns _HEAPOK and sets errno to ENOSYS.

Requirements

Routine	Required header	Optional header
`_heapset`	<malloc.h>	<errno.h>

For more compatibility information, see Compatibility in the Introduction.

Example

// crt_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>

int 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 );
}

OK - heap is fine