Access或VB VBA判断数组是否为空的几种方法

tmtony

Access或VB VBA判断数组是否为空的几种方法

方法一：Error方法

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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

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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.

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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""

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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"

zhidao

很有针对性，不错，收藏了。

zhuyiwen

学一招

t小宝

非常有用的技巧！

zpy2

很好的技巧!!

lxxgg92

不错不错 感谢

purplerose

很好，经典

李力军2

学习了