HeapFree

The HeapFree function frees a memory block allocated from a heap by the HeapAlloc or HeapReAlloc function.

BOOL HeapFree(
  HANDLE hHeap,  // handle to heap
  DWORD dwFlags, // heap free options
  LPVOID lpMem   // pointer to memory
);

Parameters

hHeap

[in] Specifies the heap whose memory block the function frees. This parameter is a handle returned by the HeapCreate or GetProcessHeap function.

dwFlags

[in] Specifies several controllable aspects of freeing a memory block. Specifying the following value overrides the corresponding value specified in the flOptions parameter when the heap was created by using the HeapCreate function.

Value	Meaning
HEAP_NO_SERIALIZE	Specifies that mutual exclusion will not be used while HeapFree is accessing the heap. Do not specify this value when accessing the process heap. The system may create additional threads within the application's process, such as a CTRL+C handler, that simultaneously access the process heap.

lpMem

[in] Pointer to the memory block to free. This pointer is returned by the HeapAlloc or HeapReAlloc function.

Return Values

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. An application can call GetLastError for extended error information.

Remarks

Serialization ensures mutual exclusion when two or more threads attempt to simultaneously allocate or free blocks from the same heap. There is a small performance cost to serialization, but it must be used whenever multiple threads allocate and free memory from the same heap. Setting the HEAP_NO_SERIALIZE value eliminates mutual exclusion on the heap. Without serialization, two or more threads that use the same heap handle might attempt to allocate or free memory simultaneously, likely causing corruption in the heap. The HEAP_NO_SERIALIZE value can, therefore, be safely used only in the following situations:

• The process has only one thread.
• The process has multiple threads, but only one thread calls the heap functions for a specific heap.
• The process has multiple threads, and the application provides its own mechanism for mutual exclusion to a specific heap.

You should not refer in any way to memory that has been freed by HeapFree. Once that memory is freed, any information that may have been in it is gone forever. If you require information, do not free memory containing the information. Function calls that return information about memory (such as HeapSize) may not be used with freed memory, as they may return bogus data.

Note  To guard against an access violation, use structured exception handling to protect any code that writes to or reads from a heap. For more information on structured exception handling with memory accesses, see Reading and Writing and Structured Exception Handling.

Requirements

  Windows NT/2000: Requires Windows NT 3.1 or later.
  Windows 95/98: Requires Windows 95 or later.
  Header: Declared in Winbase.h; include Windows.h.
  Library: Use Kernel32.lib.

See Also

Memory Management Overview, Memory Management Functions, GetProcessHeap, HeapAlloc, HeapCreate, HeapDestroy, HeapReAlloc, HeapSize, SetLastError