HeapSize

The HeapSize function returns the size, in bytes, of a memory block allocated from a heap by the HeapAlloc or HeapReAlloc function.

DWORD HeapSize(
  HANDLE hHeap,  // handle to the heap
  DWORD dwFlags, // heap size control flags
  LPCVOID lpMem  // pointer to memory to return size for
);
 

Parameters

hHeap

Specifies the heap in which the memory block resides. This handle is returned by the HeapCreate or GetProcessHeap function.

dwFlags

Specifies several controllable aspects of accessing the memory block. Only one flag is currently defined; however, all other flag values are reserved for future use. Specifying this flag will override the corresponding flag 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 HeapSize is accessing the heap. This flag should not be specified 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.

lpaam

Pointer to the memory block whose size the function will obtain. This is a pointer returned by the HeapAlloc or HeapReAlloc function.

Return Values

If the function succeeds, the return value is the size, in bytes, of the allocated memory block.

If the function fails, the return value is 0xFFFFFFFF. The function does not call SetLastError. An application cannot 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 flag 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 flag 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.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Requires version 1.0 or later.
  Header: Declared in winbase.h.
  Import Library: Use kernel32.lib.

See Also

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