1、VBA數組底層結構：

VBA的數組在底層是SafeArray：

'https://docs.microsoft.com/zh-cn/windows/win32/api/oaidl/ns-oaidl-safearraybound?redirectedfrom=MSDNType?SafeArrayBound    cElements As Long '// 該維的長度    lLbound   As Long ' // 該維的數組存取的下限，一般為0End Type'https://docs.microsoft.com/zh-cn/windows/win32/api/oaidl/ns-oaidl-safearray?redirectedfrom=MSDNType SafeArray    cDims      As Integer ' // 數組的維度    fFeatures  As Integer '    cbElements As Long ' // 數組元素的字節大小    cLocksas   As Long '    pvDataas   As Long ' // 數組的數據指針????rgsabound(0)?As?SafeArrayBoundEnd Type

如果要取數組的地址，需要用到API函數：

Public Declare Function VarPtrArray Lib "msvbvm60.dll" Alias "VarPtr" (ByRef Var() As Any) As Long

VarPtrArray 返回的并不是SafeArray的地址，我們可以進行測試：

Sub TestArray()    Dim Arr() As Byte        ReDim Arr(3) As Byte        Dim sa As SafeArray    CopyMemory VarPtr(sa), VarPtrArray(Arr), Len(sa)        Printf "sa.cDims = %d, sa.cbElements = %d", sa.cDims, sa.cbElementsEnd Sub輸出：sa.cDims = -27936, sa.cbElements = 3994212

從輸出可以看出，我們預計的sa.cDims應該=1和sa.cbElements=1并沒有出現，顯然VarPtrArray(Arr)獲取到的還不是Arr的地址。

像c語言這樣的語言，是有指針的，VBA數組的底層實現應該是使用了一個指針來引用SafeArray結構，而VarPtrArray(Arr)獲取到的應該是指針的地址。

Sub TestArray()    Dim Arr() As Byte    ReDim Arr(3) As Byte    Dim ptr As Long '保存[Arr指針]的地址        CopyMemory VarPtr(ptr), VarPtrArray(Arr), 4        Dim sa As SafeArray    CopyMemory VarPtr(sa), ptr, Len(sa)        Printf "sa.cDims = %d, sa.cbElements = %d", sa.cDims, sa.cbElementsEnd Sub輸出sa.cDims = 1, sa.cbElements = 1

從輸出可以看出，預計的sa.cDims應該=1和sa.cbElements=1出現了。

進一步測試，從pvDataas 中提取數據，看看獲取的數據是否能正確：

Sub TestArray2()    Dim Arr() As Byte    ReDim Arr(3) As Byte    Dim ptr As Long '保存[Arr指針]的地址        Arr(0) = &H88    Arr(1) = &H21    Arr(2) = &H27    Arr(3) = &H99        CopyMemory VarPtr(ptr), VarPtrArray(Arr), 4        Dim sa As SafeArray    CopyMemory VarPtr(sa), ptr, Len(sa)        Dim b(3) As Byte    Dim i As Long    For i = 0 To 3        CopyMemory VarPtr(b(i)), sa.pvDataas + sa.cbElements * i, sa.cbElements        Printf "b(%d) = 0x%x ", i, b(i)    NextEnd Sub輸出：b(0) = 0x88 b(1) = 0x21 b(2) = 0x27 b(3) = 0x99

完全正確。

2、改變SafeArray的pvDataas地址會有什么情況：

既然知道了數組的內存結構，那我們就嘗試把pvDataas改變看看會怎么樣：

Sub TestArray2()    Dim Arr() As Byte    ReDim Arr(0) As Byte    Dim ptr As Long '保存[Arr指針]的地址        CopyMemory VarPtr(ptr), VarPtrArray(Arr), 4        Dim lValue As Long    lValue = &HABCDEF99        Dim plValue As Long    plValue = VarPtr(lValue)        '修改pvDataas指向lValue    CopyMemory ptr + 12, VarPtr(plValue), 4    '修改Arr的SafeArrayBound為4    Dim cElements As Long    cElements = 4    CopyMemory ptr + 16, VarPtr(cElements), 4        Dim sa As SafeArray    CopyMemory VarPtr(sa), ptr, Len(sa)        Printf "sa.pvDataas = 0x%x, plValue = 0x%x", sa.pvDataas, plValue        Dim i As Long    For i = 0 To 3        Printf "Arr(%d) = 0x%x ", i, Arr(i)    NextEnd Sub輸出：sa.pvDataas = 0x36ecbc, plValue = 0x36ecbcArr(0) = 0x99 Arr(1) = 0xef Arr(2) = 0xcd Arr(3)?=?0xab?

定義了一個容量為1的byte數組，但是我把pvDataas的值修改成了1個Long變量的地址，同時也改變了他的SafeArrayBound為4，從輸出可以看到，這個數組已經變成了一個容量為4的byte數組。

但是End Sub后，我的電腦測試Excel崩潰，這個和前面講到的String類型里的情況差不多，到底是什么原因？

3、ReDim Preserve做了什么

我們經常會用ReDim Preserve來改變數組的容量，當然一般都是擴大。擴大的話要更多的內存空間來保存數據，所以應該是要重新分配內存，測試：

Sub TestArray()    Dim Arr() As Byte    ReDim Arr(3) As Byte    Dim ptr As Long '保存[Arr指針]的地址    Dim sa As SafeArray        CopyMemory VarPtr(ptr), VarPtrArray(Arr), 4    CopyMemory VarPtr(sa), ptr, Len(sa)    Printf "ptr = 0x%x, sa.pvDataas= 0x%x, sa.cDims = %d, sa.cbElements = %d, sa.rgsabound(0).cElements = %d", ptr, sa.pvDataas, sa.cDims, sa.cbElements, sa.rgsabound(0).cElements    ReDim Preserve Arr(4) As Byte    CopyMemory VarPtr(ptr), VarPtrArray(Arr), 4    CopyMemory VarPtr(sa), ptr, Len(sa)    Printf "ptr = 0x%x, sa.pvDataas= 0x%x, sa.cDims = %d, sa.cbElements = %d, sa.rgsabound(0).cElements = %d", ptr, sa.pvDataas, sa.cDims, sa.cbElements, sa.rgsabound(0).cElementsEnd Sub輸出：ptr = 0x16597108, sa.pvDataas= 0x167c3a40, sa.cDims = 1, sa.cbElements = 1, sa.rgsabound(0).cElements = 4ptr = 0x16597108, sa.pvDataas= 0x167c3790, sa.cDims = 1, sa.cbElements = 1, sa.rgsabound(0).cElements = 5

pvDataas已經改變，重新分配了內存空間。

但是，如果是減小呢？

我本來猜測只要修改sa.rgsabound(0).cElements的值就可以達到減小容量的目的，可測試卻同樣重新分配了內存：

Sub TestArray()    Dim Arr() As Byte    ReDim Arr(3) As Byte    Dim ptr As Long '保存[Arr指針]的地址    Dim sa As SafeArray        CopyMemory VarPtr(ptr), VarPtrArray(Arr), 4    CopyMemory VarPtr(sa), ptr, Len(sa)    Printf "ptr = 0x%x, sa.pvDataas= 0x%x, sa.cDims = %d, sa.cbElements = %d, sa.rgsabound(0).cElements = %d", ptr, sa.pvDataas, sa.cDims, sa.cbElements, sa.rgsabound(0).cElements    ReDim Preserve Arr(1) As Byte    CopyMemory VarPtr(ptr), VarPtrArray(Arr), 4    CopyMemory VarPtr(sa), ptr, Len(sa)    Printf "ptr = 0x%x, sa.pvDataas= 0x%x, sa.cDims = %d, sa.cbElements = %d, sa.rgsabound(0).cElements = %d", ptr, sa.pvDataas, sa.cDims, sa.cbElements, sa.rgsabound(0).cElementsEnd Sub輸出：ptr = 0x167d5068, sa.pvDataas= 0x167c3a50, sa.cDims = 1, sa.cbElements = 1, sa.rgsabound(0).cElements = 4ptr = 0x167d5068, sa.pvDataas= 0x167c37f0, sa.cDims = 1, sa.cbElements = 1, sa.rgsabound(0).cElements = 2

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