Using Global memory from Visual basic

Global memory is memory that can be shared between applications. It is useful if you are writing a system where multiple cooperating apps or even just to allow you to watch global variables in your own application.


private Declare Function GlobalLock Lib "kernel32" (byval hMem as Long) as Long


private Declare Function GlobalSize Lib "kernel32" (byval hMem as Long) as Long


private Declare Function GlobalUnlock Lib "kernel32" (byval hMem as Long) as Long


private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (lpvDest as Any, lpvSource as Any, byval cbCopy as Long)


private Declare Function GlobalAlloc Lib "kernel32" (byval wFlags as Long, byval dwBytes as Long) as Long


private Declare Function GlobalFree Lib "kernel32" (byval hMem as Long) as Long
private mMyData() as Byte
private mMyDataSize as Long
private mHmem as Long


public Enum enGlobalmemoryAllocationConstants
GMEM_FIXED = &H0
GMEM_DISCARDABLE = &H100
GMEM_MOVEABLE = &H2
GMEM_NOCOMPACT = &H10
GMEM_NODISCARD = &H20
GMEM_ZEROINIT = &H40
End Enum


'\\ --[CopyFromHandle]---------------------------
'\\ Copies the data from a global memory handle
'\\ to a private byte array copy
'\\ ---------------------------------------------


public Sub CopyFromHandle(byval hMemHandle as Long)
Dim lRet as Long
Dim lPtr as Long
lRet = GlobalSize(hMemHandle)


If lRet > 0 then
mMyDataSize = lRet
lPtr = GlobalLock(hMemHandle)


If lPtr > 0 then
ReDim mMyData(0 to mMyDataSize - 1) as Byte
CopyMemory mMyData(0), byval lPtr, mMyDataSize
Call GlobalUnlock(hMemHandle)
End If
End If
End Sub

'\\ --[CopyToHandle]-----------------------------
'\\ Copies the private data to a memory handle
'\\ passed in
'\\ ---------------------------------------------


public Sub CopyToHandle(byval hMemHandle as Long)
Dim lSize as Long
Dim lPtr as Long
'\\ Don't copy if its empty


If Not (mMyDataSize = 0) then
lSize = GlobalSize(hMemHandle)
'\\ Don't attempt to copy if zero size..
' .


If lSize > 0 then


If lPtr > 0 then
CopyMemory byval lPtr, mMyData(0), lSize
Call GlobalUnlock(hMemHandle)
End If
End If
End If
End Sub




HTH,
Duncan

(This functionality is wrapped up in the ApiGlobalMemory class in the EventVB.dll)

-------------------------------------------------
Ex. Datis: Duncan Jones
Merrion Computing Ltd
http://www.merrioncomputing.com
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