HeapWalk function (heapapi.h)

Article
10/13/2021

Enumerates the memory blocks in the specified heap.

Syntax

BOOL HeapWalk(
  [in]      HANDLE               hHeap,
  [in, out] LPPROCESS_HEAP_ENTRY lpEntry
);

Parameters

[in] hHeap

A handle to the heap. This handle is returned by either the HeapCreate or GetProcessHeap function.

[in, out] lpEntry

A pointer to a PROCESS_HEAP_ENTRY structure that maintains state information for a particular heap enumeration.

If the HeapWalk function succeeds, returning the value TRUE, this structure's members contain information about the next memory block in the heap.

To initiate a heap enumeration, set the lpData field of the PROCESS_HEAP_ENTRY structure to NULL. To continue a particular heap enumeration, call the HeapWalk function repeatedly, with no changes to hHeap, lpEntry, or any of the members of the PROCESS_HEAP_ENTRY structure.

Return value

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

If the heap enumeration terminates successfully by reaching the end of the heap, the function returns FALSE, and GetLastError returns the error code ERROR_NO_MORE_ITEMS.

Remarks

The HeapWalk function is primarily useful for debugging because enumerating a heap is a potentially time-consuming operation. Locking the heap during enumeration blocks other threads from accessing the heap and can degrade performance, especially on symmetric multiprocessing (SMP) computers. The side effects can last until the heap is unlocked. Use the HeapLock and HeapUnlock functions to control heap locking during heap enumeration.

To initiate a heap enumeration, call HeapWalk with the lpData field of the PROCESS_HEAP_ENTRY structure pointed to by lpEntry set to NULL.

To continue a heap enumeration, call HeapWalk with the same hHeap and lpEntry values, and with the PROCESS_HEAP_ENTRY structure unchanged from the preceding call to HeapWalk. Repeat this process until you have no need for further enumeration, or until the function returns FALSE and GetLastError returns ERROR_NO_MORE_ITEMS, indicating that all of the heap's memory blocks have been enumerated.

No special call of HeapWalk is needed to terminate the heap enumeration, since no enumeration state data is maintained outside the contents of the PROCESS_HEAP_ENTRY structure.

HeapWalk can fail in a multithreaded application if the heap is not locked during the heap enumeration.

Examples

Enumerating a Heap

Requirements

Requirement	Value
Minimum supported client	Windows XP [desktop apps only]
Minimum supported server	Windows Server 2003 [desktop apps only]
Target Platform	Windows
Header	heapapi.h (include Windows.h)
Library	Kernel32.lib
DLL	Kernel32.dll