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_heapwalk

Traverses the heap and returns information about the next entry.

int _heapwalk( 
   _HEAPINFO *entryinfo 
);

Parameter

entryinfo
Buffer to contain heap information.

Return Value

_heapwalk 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.
_HEAPBADPTR
_pentry field of _HEAPINFO structure does not contain valid pointer into heap.
_HEAPEND
End of heap reached successfully.
_HEAPEMPTY
Heap not initialized.
_HEAPOK
No errors so far; entryinfo is updated with information about the next heap entry.

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

Remarks

The _heapwalk function helps debug heap-related problems in programs. The function walks through the heap, traversing one entry per call, and returns a pointer to a structure of type _HEAPINFO that contains information about the next heap entry. The _HEAPINFO type, defined in MALLOC.H, contains the following elements:

int *_pentry
Heap entry pointer.
size_t _size
Size of heap entry.
int _useflag
Flag that indicates whether heap entry is in use.

A call to _heapwalk that returns _HEAPOK stores the size of the entry in the _size field and sets the _useflag field to either _FREEENTRY or _USEDENTRY (both are constants defined in MALLOC.H). To obtain this information about the first entry in the heap, pass _heapwalk a pointer to a _HEAPINFO structure whose _pentry member is NULL.

Note   Beginning with 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 _heapwalk is Windows NT. When it is called by any other Win32 platform, _heapwalk returns _HEAPEND and sets errno to ENOSYS.

Requirements

Routine Required header Optional headers Compatibility
_heapwalk <malloc.h> <errno.h> Win NT, Win 2000, Win XP

For additional compatibility information, see Compatibility in the Introduction.

Libraries

All versions of the C run-time libraries.

Example

// crt_heapwalk.c
/* This program "walks" the heap, starting
 * at the beginning (_pentry = NULL). It prints out each
 * heap entry's use, location, and size. It also prints
 * out information about the overall state of the heap as
 * soon as _heapwalk returns a value other than _HEAPOK.
 */

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

void heapdump( void );

int main( void )
{
   char *buffer;

   heapdump();
   if( (buffer = (char *)malloc( 59 )) != NULL )
   {
      heapdump();
      free( buffer );
   }
   heapdump();
}

void heapdump( void )
{
   _HEAPINFO hinfo;
   int heapstatus;
   hinfo._pentry = NULL;
   while( ( heapstatus = _heapwalk( &hinfo ) ) == _HEAPOK )
   { printf( "%6s block at %Fp of size %4.4X\n",
        ( hinfo._useflag == _USEDENTRY ? "USED" : "FREE" ),
          hinfo._pentry, hinfo._size );
   }

   switch( heapstatus )
   {
   case _HEAPEMPTY:
      printf( "OK - empty heap\n" );
      break;
   case _HEAPEND:
      printf( "OK - end of heap\n" );
      break;
   case _HEAPBADPTR:
      printf( "ERROR - bad pointer to heap\n" );
      break;
   case _HEAPBADBEGIN:
      printf( "ERROR - bad start of heap\n" );
      break;
   case _HEAPBADNODE:
      printf( "ERROR - bad node in heap\n" );
      break;
   }
}

Sample Output

  USED block at 00310650 of size 0100
  USED block at 00310758 of size 0800
  USED block at 00310F60 of size 0080
  FREE block at 00310FF0 of size 0398
  USED block at 00311390 of size 000D
  USED block at 003113A8 of size 00B4
  USED block at 00311468 of size 0034
  USED block at 003114A8 of size 0039
...
  USED block at 00312228 of size 0010
  USED block at 00312240 of size 1000
  FREE block at 00313250 of size 1DB0
OK - end of heap

See Also

Memory Allocation Routines | _heapadd | _heapchk | _heapmin | _heapset | Run-Time Routines and .NET Framework Equivalents

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