Recursive function returning empty string

Question

How do I properly exit a recursive function and return a value in VBA?

I have this simple code to remove multiple spaces from a string:

Public Function RemoveMultipleSpaces(s As String) As String
    If InStr(1, s, "  ", vbTextCompare) > 0 Then
        Dim newS As String
        newS = Replace(s, "  ", " ")
        RemoveMultipleSpaces (newS)
    Else
        RemoveMultipleSpaces = s
        End
    End If
End Function

But depending on what I use to exit either End or Exit Function, I either get nothing returned or an empty string.

Erik A · Accepted Answer · 2019-08-16 08:55:59Z

4

A proper recursive function doesn't need a specific exit condition. You just stop calling the function recursively, and it exits.

However, if you want to explicitly exit, you can use Exit Function.

Your mistake, however, is that when you make a recursive call, you need to return the result of the recursive call.

Public Function RemoveMultipleSpaces(s As String) As String
    If InStr(1, s, "  ", vbTextCompare) > 0 Then
        Dim newS As String
        newS = Replace(s, "  ", " ")
        RemoveMultipleSpaces = RemoveMultipleSpaces(newS)
    Else
        RemoveMultipleSpaces = s
    End If
End Function

edited Aug 16, 2019 at 8:55

answered Aug 16, 2019 at 8:53

Erik A

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3 Comments

GSerg Over a year ago

Your code modifies the byref s as well as returning the result. That is not what the OP had.

Erik A Over a year ago

@GSerg Valid, adjusted it to not modify the byref. Note this leads to storing one copy of the string for each level of recursion, which can be a burden on memory when working with large strings.

Marcos Foster Over a year ago

Oh, that makes sense! Thank you.

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