VBA基础
Access或VB VBA判断数组的值是否为空的几种方法
2017-12-04 17:46:09

在数组中，如果下标值大于存在的值。 会提示“下标越界”的错误

注意：数组下标从0开始

方法一：Error方法
就是采用通用的错误捕获功能
On Error Goto 行号       '遇到错误，转到行号处处理
On Error Resume Next '忽略错误，继续执行
On Error Goto 0           '强制取消错误捕获功能
Function IsNotEmpty(ByVal sArray As Variant) As Boolean '判断数组是否为空
        Dim i     As Long
        IsNotEmpty = True
        On Error GoTo lerr:
        i = UBound(b)
        Exit Function
lerr:
        IsNotEmpty = False
End Function

方法二：CopyMemory方法
VB的数组都是安全数组，通过访问一个结构来确定 数组内容保存位置，上标下标和维数
安全数组结构的地址可以用
Private Declare Function VarPtrArray Lib "msvbvm60.dll" Alias "VarPtr" (ByRef Ptr() As Any) As Long
Private Declare Sub CopyMemory Lib "kernel32.dll" Alias "RtlMoveMemory" _
             (ByRef Destination As Any, ByRef Source As Any, ByVal Length As Long)
安全数组的头两位就保存着维数信息
Option Explicit
Private Declare Function VarPtrArray Lib "msvbvm60.dll" Alias "VarPtr" (ByRef Ptr() As Any) As Long
Private Declare Sub CopyMemory Lib "kernel32.dll" Alias "RtlMoveMemory" (ByRef Destination As Any, ByRef Source As Any, ByVal Length As Long)
Private Sub Form_Load()
    Dim MyArr() As Long
    Dim pMyarr As Long
    Dim nDims As Integer
    '从数据指针得到SafeArray结构的指针
    CopyMemory pMyarr, ByVal VarPtrArray(MyArr), 4
    If pMyarr = 0 Then
        MsgBox "这个数组是空数组"
        '再从这个指针所指地址的头两个字节取出cDims
        CopyMemory nDims, ByVal pMyarr, 2
        MsgBox "这个数组有" & nDims & "维"
    End If
End Sub

方法三：使用api函数safearraygetdim()的返回值，返回值值<=0,说明数组元素个数为0或者数组还没有初始化.
SafeArrayGetDim用来判断一个数组的维数，该函数在MSDN中定义为：
UINT SafeArrayGetDim(
  SAFEARRAY FAR* psa
转换维VB中的语法格式为：
Public Declare Function SafeArrayGetDim Lib "oleaut32.dll" (ByRef saArray() As Any) As Long
如果数组已经初始化，则返回非0，否则返回0。
'API判断数组为空或没有初始化
Sub diag()
Dim msg As String
Dim arr1() As String, arr2() As String, arr3() As Date, arr4() As Date, arr5() As Range, arr6() As Range
msg = "arr1 " & IIf(SafeArrayGetDim(arr1) > 0, "数组不为空!", "数组为空!")
arr2 = Split("一、二、三、四、五、六", "、")
msg = msg & vbCrLf & "arr2 " & IIf(SafeArrayGetDim(arr2) > 0, "数组不为空!", "数组为空!")
msg = msg & vbCrLf & "arr3 " & IIf(SafeArrayGetDim(arr3) > 0, "数组不为空!", "数组为空!")
ReDim arr4(1 To 100)
msg = msg & vbCrLf & "arr4 " & IIf(SafeArrayGetDim(arr4) > 0, "数组不为空!", "数组为空!")
ReDim arr6(1 To 256, 1 To 65536)
msg = msg & vbCrLf & "arr5 " & IIf(SafeArrayGetDim(arr5) > 0, "数组不为空!", "数组为空!")
msg = msg & vbCrLf & "arr6 " & IIf(SafeArrayGetDim(arr6) > 0, "数组不为空!", "数组为空!")
MsgBox msg
End Sub

方法四：使用cstr(Join(list[, delimiter]))函数的返回值是否不等于""
将delimiter参数设置为""
例如:if (cstr(join(arr,""))) = "" then msgbox "arr 数组为空或者尚未初始化"

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