CopyMemory 如果不放入函数，Excel 会崩溃

Question

我在试验CopyMemory时遇到了一个奇怪的问题。我有一段从 Bytecomb 复制的代码，只有当我把它放入一个函数中时才有效：

我把这个放在开头：

Declare PtrSafe Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (pDest As Any, pSource As Any, ByVal ByteLen As Long)

工作版本：

Sub StringTest()
Dim str1 As String
Dim pstr1 As LongPtr
str1 = "PowerVB"
Debug.Print "Memory  : 0x"; Mem_ReadHex(pstr1 - 4, LenB(str1) + 6)
End Sub
Public Function Mem_ReadHex(ByVal Ptr As LongPtr, ByVal Length As Long) As String
Dim bBuffer() As Byte, strBytes() As String, i As Long, ub As Long, b As Byte
ub = Length - 1
ReDim bBuffer(ub)
ReDim strBytes(ub)
CopyMemory bBuffer(0), ByVal Ptr, Length
For i = 0 To ub
b = bBuffer(i)
strBytes(i) = IIf(b < 16, "0", "") & Hex$(b)
Next
Mem_ReadHex = Join(strBytes, "")
End Function

该程序完美地打印出内存中字符串的整个布局(前 4 个字节表示长度，然后是字符串内容，然后是 2 个字节的 null(：

Memory  : 0x0E00000050006F00770065007200560042000000

现在如果我将函数放入 sub 中，它会崩溃：

Sub StringTest()
Dim str1 As String
Dim str2 As String
Dim pstr1 As LongPtr
str1 = "PowerVB"
CopyMemory pstr1, ByVal VarPtr(str1), 8
Dim bBuffer() As Byte, strBytes() As String
ub = LenB(str1) + 5
ReDim bBuffer(ub)
ReDim strBytes(ub)
CopyMemory bBuffer(0), ByVal pstr1 - 4, LenB(str1) + 6 'extra 4 bytes for string length, and 2 bytes of null characters
For i = 0 To ub
b = bBuffer(i)
strBytes(i) = IIf(b < 16, "0", "") & Hex$(b) 'for 2 bytes, if the value < 16, then it only consists of one byte
Next i
Debug.Print Join(strBytes, "")
End Sub

我不明白。两个版本有什么区别？

Answer 1

好的，我找到了修复程序：

CopyMemory bBuffer(0), ByVal pstr1 - 4, ub + 1

因为 CopyMemory 必须将long作为第三个参数，所以我不能使用LenB(str1) + 6，因为它可能是一个整数。