WD98: Error Message Using Mid(), Left() or Right() Function (181103)

CAUSE

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This problem occurs when the length parameter for the statement is negative.

NOTE: In Word 2.0 for Windows, a negative value in the count parameter of the Mid$(), Right$() or Left$() functions is ignored and does not generate an error.

The Mid() function returns a portion of a text string starting at a given character position. The syntax for the command is where <string> is the text string to search, <start> is the character position from which to start, and <length> is the number of characters to return. If no <length> parameter is specified, or if there are fewer than <length> characters in the text, the function returns all the characters from the <start> position to the end of the string.

The following sample macro illustrates the error message described in the "Symptoms" section of this article:

   Sub ErrorOccurs()
      Dim Test As String
      Test = Mid("hello", 1, -1)
      MsgBox Test
   End Sub
				

The following sample macro returns the error because the length of the string variable Test minus one is a negative number (0 - 1 = -1):

   Sub ErrorOccurs()
      Dim Test As String
      Dim ReturnText As String
      Test = ""
      ' Empty string, could be passed as an empty dialog
      ' variable, for example.
      ReturnText = Mid(Test, Len(Test) - 1)
   End Sub
				

NOTE: Word version 2.0 for Windows ignores a -1 value for the <length> parameter. So in Word 2.0 all the characters from the first character position to the end of the string are displayed in the message box. In the first example, the string "hello" is displayed.

   Sub ErrorDoesNotOccur()
      Dim Test As String
      Dim ReturnText As String
      ' Empty string, could be passed as an empty dialog
      ' variable, for example.
      Test = ""
      ' Test the length of the string to ensure
      ' that subtracting 1 from the length leaves
      ' at least 1 character.
      If Len(Test) - 1 > 0 then
         ReturnText = Mid(Test, Len(Test) - 1)
      End If
   End Sub