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   ► KBTo/From GuidesVB ClassicOperators  Print This     

Empty String Check (Cross Ref > Operators)

By Mike Prestwood

VB Classic versus C++/CLI: A side by side comparison between VB Classic and C++/CLI.


A language symbol used for assignment, comparison, computational, or as a logical.

Empty String Check

[Other Languages] 

Languages Focus

An empty string is a zero length string, a string that is equal to null (""), or not assigned. In some languages, you can check if a string is empty by comparing it to an empty string (""). Some languages distinguish between nil and null ("") so checking if the length is 0 is easier.

VB Classic:   Len(s&vbNullString)

In VB Classic, you have to add an empty string to the value being compared in order to get consistent results. For example, add &"" to your string varilable or it's code equivalent &vbNullString. Then compare to an empty string or verify it's length to 0 with Len.

Syntax Example:

All these will work for variables unassigned, set to "", or set to Null:

If s&"" = "" Then
MsgBox ("Quotes with &'' say null is empty")
End If
If Len(s&"") = 0 Then
MsgBox ("Len with &'' says null is empty")
End If
If Len(s&vbNullString) = 0 Then
MsgBox ("Using vbNullString also works!")
End If
C++/CLI:   String.IsNullOrEmpty

The .Net framework offers a static method in the string class: String.IsNullOrEmpty.

Syntax Example:
String^ s;
//s = ""; //Uncomment to test 2nd case.
if (String::IsNullOrEmpty(s))
  MessageBox::Show("empty string");

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