LocalReAlloc

Changes the size or the attributes of a specified local memory object. The size can increase or decrease. This function can also be used to discard a movable discardable block.

HLOCAL WINAPI LocalReAlloc(
HLOCAL hMem,
UINT uBytes,
UINT uFlags
);

hMem – Handle to the local memory object to be reallocated. This handle is returned by the LocalAlloc or a previous LocalReAlloc function.

uBytes – New size, in bytes, of the memory block. If uFlags specifies the LMEM_MODIFY flag, this parameter is ignored.

uFlags – Specifies how to reallocate the local memory object. If the LMEM_MODIFY flag is specified, this parameter modifies the attributes of the memory object, and the uBytes parameter is ignored. Otherwise, this parameter controls the reallocation of the memory object.

The LMEM_MODIFY flag can be combined with the following flags:

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

If uBytes is zero: Discards a previously movable and discardable memory block. The function fails if the object's lock count is not zero or the block is not movable and discardable. The handle remains valid.\

If uBytes is non-zero: 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 in the hMem parameter. If the object is movable, the block can be moved without invalidating the handle, even if the object is currently locked. |

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

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

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

If the function reallocates a movable object, the return value is a handle. To convert the handle to a pointer, use the LocalLock function.

If the function 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 .

When uBytes is zero and the LMEM_MOVEABLE flag is used, the function discards the block. The handle remains valid and can be used later to re-allocate the block .

In 16-bit Windows, if the data segment that contains the heap is moveable, calling this function may cause the data segment to move if Windows must increase the size of the heap and cannot do so in its current location. An application can prevent this by calling the LockData function .

#include <windows.h>
 
HLOCAL hMem = NULL;
LPSTR lpData = NULL;
 
// Allocate a fixed block of 100 bytes
hMem = LocalAlloc(LPTR, 100);
 
// Increase the size to 200 bytes, allow the block to move, and zero-init new memory
hMem = LocalReAlloc(hMem, 200, LMEM_MOVEABLE | LMEM_ZEROINIT);
 
// Convert a fixed block to movable (this is done by reallocating with the same size)
// Note: This does not use LMEM_MODIFY with LMEM_MOVEABLE, which is illegal.
hMem = LocalReAlloc(hMem, LocalSize(hMem), LMEM_MOVEABLE);
 
// Discard a movable discardable block
LocalReAlloc(hMem, 0, LMEM_MOVEABLE);

; AX = hMem, BX = new size, CX = flags
push ax
push bx
push cx
call LocalReAlloc

LocalAlloc

LocalFree

LocalLock

LocalDiscard

LocalSize

LockData