VBA - 创建空数组
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VBA - Create empty array
提问by Jonas
I have a function that takes an array of strings and map each string to a Dateinstance. The function boils down to the following code.
我有一个函数，它接受一个字符串数组并将每个字符串映射到一个Date实例。该函数归结为以下代码。
Private Function ParseDates(dates() As String) As Date()
Dim res() As Date
Dim i As Integer
If UBound(dates) >= 0 Then
ReDim res(UBound(dates)) As Date
End If
For i = LBound(dates) To UBound(dates)
res(i) = #01/01/2000#
Next i
ParseDates = res
End Function
The function works just fine as long as the argument datesis nonempty. When datesis empty resis not given a dimension. As a result, the returned value is not enumerable causing to users of this function to crash if the result is enumerated in a loop.
只要参数dates为nonempty ，该函数就可以正常工作。当dates为空时res不给定维度。因此，如果在循环中枚举结果，则返回值不可枚举，导致此函数的用户崩溃。
parsedDates = ParseDates(input)
For i = 1 To UBound(parsedDates) ' Suscription out of range
...
How do I instantiate and return an empty array, when dates is empty?
当日期为空时，如何实例化并返回一个空数组？
If you call Split("",".")you receive an object with type String(0 to -1). I need my function to return a object of type Date(0 to -1)as Date()is not an actual array.
如果你打电话，Split("",".")你会收到一个类型为 的对象String(0 to -1)。我需要我的函数返回一个类型的对象，Date(0 to -1)因为Date()它不是一个实际的数组。
I have tried with ReDim res(-1)this causes an Subscript out of rangeerror.
我试过ReDim res(-1)这会导致Subscript out of range错误。
采纳答案by Nathan_Sav
I've used something like this in the past.
我过去使用过类似的东西。
Public Function IS_ARRAY_EMPTY(arrInput As Variant) As Boolean
Dim lngTemp As Long
On Error GoTo eHandle
lngTemp = UBound(arrInput)
IS_ARRAY_EMPTY = False
Exit Function
eHandle:
IS_ARRAY_EMPTY = True
End Function
回答by Rich Holton
This seems to do the trick:
这似乎可以解决问题：
Private Declare Function EmptyDateArray Lib "oleaut32" Alias "SafeArrayCreateVector" (Optional ByVal vt As VbVarType = vbDate, Optional ByVal lLow As Long = 0, Optional ByVal lCount As Long = 0) As Date()
Function emptyDate() as Date()
emptyDate = EmptyDateArray()
End Function
Based on an answer by user wgwetofor this questionat VBForums.
基于用户wgweto在 VBForums 上对这个问题的回答。
回答by John Coleman
You specifically mentioned problems in which the calling code needs to iterate over the return value and that iterating over a non-dimensioned array throws an error. Collections don't have that problem. One possibility would be to refactor your code so that it returns a collection (which might or might not have zero elements):
您特别提到了调用代码需要迭代返回值以及迭代无维数组会引发错误的问题。集合没有这个问题。一种可能性是重构您的代码，使其返回一个集合（可能有也可能没有零元素）：
Private Function ParseDates(dates() As String) As Collection
Dim res As New Collection
Dim i As Long
For i = LBound(dates) To UBound(dates)
res.Add #1/1/2000#
Next i
Set ParseDates = res
End Function
Say the calling code has the line:
假设调用代码有以下行：
Set C = ParseDates(dates)
Even if C.Count = 0, the following loop works:
即使C.Count = 0，以下循环也有效：
Dim d As Variant
For Each d In C
'process d
Next d
回答by Moreno
Try this:
尝试这个：
Private Function ParseDates(dates() As String) As Date()
Dim res() As Date
Dim i As Integer
Dim k%
k=0
If UBound(dates) >= 0 Then
ReDim res(UBound(dates)) As Date
End If
For i = LBound(dates) To UBound(dates)
if dates(i)<>"" then
k=k+1
redim preserve res(k)
end if
res(k) = #01/01/2000#
Next i
if k=0 then
redim res(ubound(dates))
end if
ParseDates = res
End Function
