The HeapReAlloc function reallocates a block of memory from a heap. This function enables you to resize a memory block and change other memory block properties. The allocated memory is not movable.
LPVOID HeapReAlloc(
HANDLE hHeap, // handle to a heap block
DWORD dwFlags, // heap reallocation flags
LPVOID lpMem, // pointer to the memory to reallocate
DWORD dwBytes // number of bytes to reallocate
);
| Flag | Meaning |
|---|---|
| HEAP_GENERATE_EXCEPTIONS | Specifies that the operating-system raises an exception to indicate a function failure, such as an out-of-memory condition, instead of returning NULL. |
| HEAP_NO_SERIALIZE | Specifies that mutual exclusion is not used while HeapReAlloc 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. |
| HEAP_REALLOC_IN_PLACE_ONLY | Specifies that there can be no movement when reallocating a memory block to a larger size. If this flag is not specified and the reallocation request is for a larger size, the function may move the block to a new location. If this flag is specified and the block cannot be enlarged without moving, the function fails, leaving the original memory block unchanged. |
| HEAP_ZERO_MEMORY | If the reallocation request is for a larger size, this flag specifies that the additional region of memory beyond the original size be initialized to zero. The contents of the memory block up to its original size are unaffected. |
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 value.
If the function succeeds, the return value is a pointer to the reallocated memory block.
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:
| Value | Meaning |
|---|---|
| STATUS_NO_MEMORY | The reallocation attempt failed for lack of available memory. |
| STATUS_ACCESS_VIOLATION | The reallocation attempt failed because of heap corruption or improper function parameters. |
If the function fails, it calls SetLastError. An application can call GetLastError for extended error information.
If HeapReAlloc 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 reallocated block, use the HeapSize function.
If HeapReAlloc fails, the original memory is not freed, and the original handle and pointer are still valid.
To free a block of memory allocated by HeapReAlloc, use the HeapFree function.
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:
Windows CE: Windows CE does not support the HEAP_GENERATE_EXCEPTIONS value for the dwFlags parameter.
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.
Memory Management Overview, Memory Management Functions, GetProcessHeap, HeapAlloc, HeapCreate, HeapDestroy, HeapFree, HeapSize, SetLastError