Is There Anything in that String? -- Visual Studio Magazine

.NET Tips and Tricksby Peter Vogel

Is There Anything in that String?

String variables look like value types, those variables holding integers and dates. But, under the hood, strings are more like reference types, those variables that point to objects. This means that you can set a string to Nothing/null, something you can't do with integers (though you can with a variation on some value types). While a string variable set to Nothing/null is obviously a string with 'nothing there,' you probably also consider a string set to String.Empty or "" (a zero-length string, or ZLS) as 'nothing there.' In some conditions, you may even consider a bunch of blanks (" ") as 'nothing there.'

.NET provides a method for checking these conditions, and .NET 4 adds a new version that does a little more. The earlier method is the static/shared method IsNullOrEmpty, which returns True if a string is set to any of String.Empty, null/Nothing or a ZLS, but returns false for a string of blanks:

Dim res As Boolean
Dim tester As String
tester = Nothing
res = String.IsNullOrEmpty(tester) 'res is True
tester = String.Empty
res = String.IsNullOrEmpty(tester) 'res is True
tester = ""
res = String.IsNullOrEmpty(tester) 'res is True
tester = "    "
res = String.IsNullOrEmpty(tester) 'res is False

.NET 4 adds a new method named IsNullOrWhitespace which does the same thing as IsNullOrEmpty, but also returns True for a string of blanks or anything else that .NET classifies as whitespace. Whitespace is anything that returns True from char.IsWhiteSpace and includes, for example, tabs and carriage returns/linefeeds:

tester = vbTab
res = String.IsNullOrWhiteSpace(tester) 'res is True

The key issue in choosing between the two is whether you consider a string of blanks/tabs/carriage returns/linefeeds as 'nothing there' (use IsNullOrWhitespace) or as 'something there' (use IsNullOrEmpty).

Posted by Peter Vogel on 09/11/2013

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