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This function allocates a block of memory from a heap. The allocated memory is not movable.
LPVOID HeapAlloc( HANDLE hHeap, DWORD dwFlags, DWORD dwBytes );
Parameters
Value | Description |
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HEAP_NO_SERIALIZE | Specifies that mutual exclusion will not be used while the HeapAllocfunction 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 that simultaneously access the process heap. |
HEAP_ZERO_MEMORY | Specifies that the allocated memory will be initialized to zero. Otherwise, the memory is not initialized to zero. |
Return Values
A pointer to the allocated memory block indicates success. NULL indicates failure.
If the function fails, it does not call SetLastError. An application cannot call GetLastErrorfor extended error information.
Remarks
If HeapAllocsucceeds, 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 HeapSizefunction.
To free a block of memory allocated by HeapAlloc, use the HeapFreefunction.
Memory allocated by HeapAllocis not movable. Because the memory is not movable, it is possible for the heap to become fragmented.
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:
Requirements
Runs on | Versions | Defined in | Include | Link to |
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Windows CE OS | 1.0 and later | Winbase.h |
Note This API is part of the complete Windows CE OS package as provided by Microsoft. The functionality of a particular platform is determined by the original equipment manufacturer (OEM) and some devices may not support this API.
See Also
GetLastError, GetProcessHeap, HeapCreate, HeapDestroy, HeapFree, HeapReAlloc, HeapSize, SetLastError