Error handling in functions

Guys,

I have a question about error handling in simple functions like the following:

Code:

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Function fcnGetToken(str As String, strDelimiter As String, lngTokenNumber As Long) As String
'Function to return a token from a delimited string (1-based).
'E.g. fcnGetToken("14|Hello world!|123", "|", 2) = Hello world!
Dim strToken As String
  'Ensure string has been supplied
  Debug.Assert Len(str) > 0
  'Ensure delimiter has been supplied
  Debug.Assert Len(strDelimiter) > 0
  'Ensure delimiter exists in string
  Debug.Assert InStr(str, strDelimiter) <> 0
  'Ensure lngTokenNumber exists in string
  Debug.Assert (lngTokenNumber - 1) <= UBound(Split(str, strDelimiter))
  strToken = Split(str, strDelimiter)(lngTokenNumber - 1) 'Split() is zero-based
  fcnGetToken = strToken
lbl_Exit:
  Exit Function
End Function

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Say I have been using the Debug.Assert statements throughout testing to ensure that accepted values are being fed in, and everything seems fine. If for some reason after testing, when the .Assert statements are turned off, the function accepts a value which is unprepared for and will cause problems down the line - what should the course of action be?

Write an error log and stop execution?

Joe

As written, the Function declaration itself will return an error if any parameter is not present.

All below require

Code:

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    Exit Function
ErrHandler:
MsgBox ErrMsg
End Function

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Code:

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'Ensure delimiter exists in string
If Instr(Str, Delimiter) = 0 Then
ErrMsg = "The delimiter is not found in the input string"
Goto ErrHandler
End if

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Code:

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'Ensure lngTokenNumber exists in string
If (lngTokenNumber - 1) < UBound(Split(str, strDelimiter)) then
ErrMsg = "The Token number is too big"
Goto ErrHandler
End if

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Code:

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Sub Test()
  MsgBox fcnGetToken("A|B|C|D", 2)
  MsgBox fcnGetToken("A|B|C|D", 7)
  MsgBox fcnGetToken("A|B|C|D", 1, "*")
End Sub
Function fcnGetToken(str As String, lngTokenNumber As Long, Optional strDelimiter As String = "|") As String
  On Error GoTo Err_Handler
  If InStr(str, strDelimiter) > 0 Then
    fcnGetToken = Split(str, strDelimiter)(lngTokenNumber - 1)
  Else
    Err.Raise 5
  End If
lbl_Exit:
    Exit Function
Err_Handler:
  Select Case Err.Number
    Case 9
      fcnGetToken = "Token number out of range"
      Resume lbl_Exit
    Case 5
      fcnGetToken = "Argument (delimiter) not valid"
      Resume lbl_Exit
    Case Else
      'As required
  End Select
End Function

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SamT, Greg...thanks for that.