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Why is optional char argument nothing, not empty string?

Posted on 2010-09-15
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Last Modified: 2013-11-07
I have the following vb.net routine in an asp.net page:
   Private Sub GetGridData( _
         Optional ByVal sStatus As String = "New", _
         Optional ByVal sBookmark As Char = "")

      Dim sSQL As String
      Dim sWHERE As String = "WHERE 1=1 "

      If sStatus <> "Enabled" Then
         sBookmark = ""
         dlBookmark.Visible = False
      Else
         ' Do something else
         sBookMark = "x"
      End If

      sSQL = "SELECT * FROM MySQLView " & sWHERE

      If sBookmark <> "" Then
         ' FixSQL wraps single quotes around a string
         sSQL &= "AND Left(Name, 1) = " & FixSQL(sBookmark) & " "
      End If

      sSQL &= "ORDER BY Status, Name"

      Dim dr As SqlDataReader = dbHelper.OpenDataReader(sSQL)

      MyDataGrid.DataSource = dr
      MyDataGrid.DataBind()
   End Sub

Open in new window


This code no longer works when called as follows:
   GetGridData()

Open in new window


sBookmark has a value of nothing in the routine, not "", even after being assigned to string.empty. I know this used to work and I'm wondering if a change earlier this year from 1.1 to 2.0 / 3.0 / 3.5 treats chars differently. I can fix the code using a string instead of a char but I'm not sure why the car isn't set to an empty string either by the optional argument value or by the explicit assignment when status <> "Enabled".

Thanks in advance.
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Question by:ZekeLA
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2 Comments
 
LVL 75

Accepted Solution

by:
käµfm³d   👽 earned 1000 total points
ID: 33686748
There does not exist a character which equates to "empty". Strings can be empty, but characters cannot. The closes you can get is the null character, which is what I believe VB is assigning to your sBookmark.
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Author Comment

by:ZekeLA
ID: 33686910
OK. What's strange is I checked my source control repository and this code hasn't changed in 4 years. But I know it used to work. Thanks.
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