function allocates a block of memory from a heap. The allocated memory is not
| HANDLE hHeap,
||// handle to the private heap block
| DWORD dwFlags,
||// heap allocation control flags
| DWORD dwBytes
||// number of bytes to allocate
Specifies the heap from which the memory will be allocated. This parameter is
a handle returned by the HeapCreate
Specifies several controllable aspects of heap allocation. Specifying any of
these flags will override the corresponding flag specified when the heap was
created with HeapCreate
. You can specify one or more of the following flags:
||Specifies that the operating system will raise an exception to indicate a
function failure, such as an out-of-memory condition, instead of returning NULL.
||Specifies that mutual exclusion will not be used while this function is
accessing the heap. For more information about HEAP_NO_SERIALIZE, see the Remarks
section of HeapCreate.
||Specifies that the allocated memory will be initialized to zero.
Specifies the number of bytes to be allocated.
If the heap specified by the hHeap
parameter is a "non-growable" heap, dwBytes must be less than 0x7FFF8. You
create a non-growable heap by calling the HeapCreate function with a nonzero
If the function succeeds, the return value is a pointer to the allocated
If the function fails and you have not specified HEAP_GENERATE_EXCEPTIONS, the
return value is NULL.
If the function fails and you have specified HEAP_GENERATE_EXCEPTIONS, the
function may generate the following exceptions:
||The allocation attempt failed because of a lack of available memory or heap
||The allocation attempt failed because of heap corruption or improper function
Note that heap corruption can lead to either exception. It depends upon the
nature of the heap corruption.
If the function fails, it does not call SetLastError
. An application cannot call GetLastError
for extended error information.
succeeds, it allocates at least the amount of memory requested. If the actual
amount allocated is greater than the amount requested, the process can use the
entire amount. To determine the actual size of the allocated block, use the HeapSize
To free a block of memory allocated by HeapAlloc
, use the HeapFree
Memory allocated by HeapAlloc
is not movable. Since the memory is not movable, it is possible for the heap
to become fragmented.
Note that if HEAP_ZERO_MEMORY is not specified, the allocated memory will not
be initialized to zero.
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