关于RtlMoveMemory(CopyMemory)的VBA代码调试求助

Let's break down why your code isn't updating the value of c as expected, and fix it step by step.

The Core Issue #

Your CopyMemory calls are misusing pointer addresses—you're copying the address values themselves instead of the data those pointers point to. Here's where you went wrong:

1. In the first CopyMemory call, you're writing the address of c (stored in pointerOfi) into the memory location of tempvalue, not reading the actual value of c.
2. In the second call, you're writing the address of tempvalue back into pointerOfi, not writing the updated tempvalue back to c's memory space.

Corrected Code #

First, let's adjust the CopyMemory declaration to better match how RtlMoveMemory works (it expects raw pointer addresses, so using ByVal for pointer parameters is more accurate):

Option Explicit

#If VBA7 Then
Declare PtrSafe Sub CopyMemory Lib "kernel32.dll" Alias "RtlMoveMemory" ( _
    ByVal Destination As LongPtr, _
    ByVal Source As LongPtr, _
    ByVal Length As LongPtr _
)
#Else
Declare Sub CopyMemory Lib "kernel32.dll" Alias "RtlMoveMemory" ( _
    ByVal Destination As Long, _
    ByVal Source As Long, _
    ByVal Length As Long _
)
#End If

Sub Main2()
    Dim c As Long, d As Long
    c = 3
    Move2 VarPtr(c)
    Debug.Print c ' Now outputs 4 as expected!
End Sub

Sub Move2(ByVal pointerOfi As LongPtr)
    Dim tempvalue As Long
    
    ' 1. Read the value from c's memory address (stored in pointerOfi) into tempvalue
    CopyMemory tempvalue, ByVal pointerOfi, LenB(tempvalue)
    
    ' 2. Increment the temporary value
    tempvalue = tempvalue + 1
    
    ' 3. Write the updated value back to c's memory address
    CopyMemory ByVal pointerOfi, tempvalue, LenB(tempvalue)
End Sub

What Changed? #

• Reading the value: CopyMemory tempvalue, ByVal pointerOfi, LenB(tempvalue) tells CopyMemory to take the address stored in pointerOfi (the location of c), read 4 bytes (the size of a Long), and store that data in tempvalue.
• Writing the value: CopyMemory ByVal pointerOfi, tempvalue, LenB(tempvalue) reverses the process—it takes the updated data in tempvalue and writes it back to the original memory address of c, modifying the variable directly.

Alternative (Using VarPtr Explicitly) #

If you prefer to use VarPtr to specify addresses directly (instead of relying on VBA to pass variable addresses implicitly), this version works identically:

Sub Move2(ByVal pointerOfi As LongPtr)
    Dim tempvalue As Long
    
    CopyMemory VarPtr(tempvalue), pointerOfi, LenB(tempvalue)
    tempvalue = tempvalue + 1
    CopyMemory pointerOfi, VarPtr(tempvalue), LenB(tempvalue)
End Sub

内容的提问来源于stack exchange，提问作者Solus161