GlobalReAlloc

The GlobalReAlloc function changes the size or attributes of a specified global memory object. The size can increase or decrease.

HGLOBAL GlobalReAlloc(

HGLOBAL hMem,	// handle to the global memory object
DWORD dwBytes,	// new size of the block
UINT uFlags	// how to reallocate object
);

Parameters

hMem

Identifies the global memory object to be reallocated. This handle is returned by either the GlobalAlloc or GlobalReAlloc function.

dwBytes

Specifies the new size, in bytes, of the memory block. If this parameter is zero and the uFlags parameter specifies the GMEM_MOVEABLE flag, the function returns the handle of a memory object that is marked as discarded. If uFlags specifies the GMEM_MODIFY flag, this parameter is ignored.

uFlags

Specifies how to reallocate the global memory object. If the GMEM_MODIFY flag is specified, this parameter modifies the attributes of the memory object, and the dwBytes parameter is ignored. Otherwise, this parameter controls the reallocation of the memory object.

The GMEM_MODIFY flag can be combined with either or both of the following flags:

Flag	Meaning
GMEM_DISCARDABLE	Allocates discardable memory if the GMEM_MODIFY flag is also specified. This flag is ignored, unless the object was previously allocated as movable or the GMEM_MOVEABLE flag is also specified.
GMEM_MOVEABLE	Windows NT only: Changes a fixed memory object to a movable memory object if the GMEM_MODIFY flag is also specified.

If this parameter does not specify GMEM_MODIFY, it can be any combination of the following flags:

Flag	Meaning
GMEM_MOVEABLE	If dwBytes is zero, discards a previously movable and discardable memory block. If the lock count of the object is not zero or if the block is not movable and discardable, the function fails. If dwBytes is nonzero, enables the system to move the reallocated block to a new location without changing the movable or fixed attribute of the memory object. If the object is fixed, the handle returned may be different from the handle specified by the hMem parameter. If the object is movable, the block can be moved without invalidating the handle, even if the object is currently locked by a previous call to the GlobalLock function. To get the new address of the memory block, use GlobalLock.
GMEM_NOCOMPACT	Prevents memory from being compacted or discarded to satisfy the allocation request.
GMEM_ZEROINIT	Causes the additional memory contents to be initialized to zero if the memory object is growing in size.

Return Values

If the function succeeds, the return value is the handle of the reallocated memory object.

If the function fails, the return value is NULL. To get extended error information, call GetLastError.

Remarks

If GlobalReAlloc reallocates a movable object, the return value is the handle of the memory object. To convert the handle to a pointer, use the GlobalLock function.

If GlobalReAlloc reallocates a fixed object, the value of the handle returned is the address of the first byte of the memory block. To access the memory, a process can simply cast the return value to a pointer.

If GlobalReAlloc fails, the original memory is not freed, and the original handle and pointer are still valid.

See Also

GlobalAlloc, GlobalFree, GlobalLock

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