GlobalLock Function

Declare Function GlobalLock Lib "kernel32.dll" (ByVal hMem As Long) As Long

Platforms: Win 32s, Win 95/98, Win NT

GlobalLock locks a moveable block of memory into its current physical position. The block's internal lock count is incremented by one; a memory block is considered locked if its lock counter is greater than zero. Memory blocks cannot be moved or discarded while locked. The function returns a pointer to the beginning of the memory block if successful, or 0 if the function fails.

hMem

The handle to the moveable memory block to lock.

Example:

' Use a block of memory as an intermediary step to copy
' the contents of array s() to array t().  Yes, you could copy them directly,
' but this demonstrates a few different memory functions.
Dim s(0 To 255) As Integer, t(0 To 255) As Integer  ' arrays to copy from/to
Dim c As Integer, retval As Long  ' counter variable & return value
Dim hMem As Long, pMem As Long  ' handle and pointer to memory block

' Initialize the source array s()'s data
For c = 0 To 255
  s(c) = 2 * c  ' each element equals double its index
Next c

' Allocate a moveable block of memory (returns a handle) (Integer type = 2 bytes)
hMem = GlobalAlloc(GMEM_MOVEABLE Or GMEM_ZEROINIT, 256 * 2)
' Lock the memory block, returning a pointer to it
pMem = GlobalLock(hMem)
' Copy the entire contents of s() to the memory block
' Note that pMem is ByVal because we want its contents, not a pointer to it
CopyMemory ByVal pMem, s(0), 256 * 2
' Copy the contents of the memory block to t()  (we could have just copied s() to t())
CopyMemory t(0), ByVal pMem, 256 * 2
' Unlock the memory block, destroying the pointer and freeing resources
x = GlobalUnlock(hMem)
' Free the memory block (de-allocate it)
x = GlobalFree(hMem)

' Verify that t() = s(), which it should
For c = 0 To 255
  If s(c) <> t(c) Then Debug.Print "Copy attempt failed."
End If

See Also: GlobalUnlock
Category: Memory

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