Indicates whether the specified string is null or an Empty string. Namespace: System Assembly: mscorlib (in mscorlib.dll) Is Null Or Empty is a convenience method that enables you to simultaneously test whether a String is null or its value is Empty. It is equivalent to the following code: result = s = null | s = String. Empty; You can use the Is Null Or White Space method to test whether a string is null, its value is String. Empty, or it consists only of white-space characters. A string is null if it has not been assigned a value (in C+ and Visual Basic) or if has explicitly been assigned a value of null. Although the composite formatting feature can gracefully handle a null string, as the following example shows, attempting to call one if its members throws a Null Reference Exception. using System; public class Example public static void Main String s = null; Console. Write Line( The value of the string is ' 0 ', s try Console. Write Line( String length is 0, s. Length catch ( Null Reference Exception e) Console. Write Line(e. Message / The example displays the following output: / The value of the string is ' / Object reference not set to an instance of an object. A string is empty if it is explicitly assigned an empty string ( ) or String. Empty. An empty string has a Length of 0. The following example creates an empty string and displays its value and its length. String s = ; Console. Write Line( The length of ' 0 ' is 1., s, s. Length / The example displays the following output: / The length of ' is 0. The following example examines three strings and determines whether each string has a value, is an empty string, or is null. using System; class Sample public static void Main string s1 = abcd ; string s2 = ; string s3 = null; Console. Write Line( String s1 0., Test(s1 Console. Write Line( String s2 0., Test(s2 Console. Write Line( String s3 0.
Nothing would be no string at all (null in other languages which is different than an empty string ( which is actually a string. However, the check should be replaced with If Not String. Is Null Or Empty( Test String) Then, which makes it clearer what exactly you are doing. I just played around with this some in LINQPad, and found something mildly surprising. In VB. NET: Dim s1 as string = Nothing Dim s2 as string = Console. Write Line(s1 is Nothing) ' True Console. Write Line(s2 is Nothing) ' False Console. Write Line(s1 = ) ' True Console. Write Line(s2 = ) ' True Console. Write Line(string. Is Null Or Empty(s1) ' True Console. Write Line(string. Is Null Or Empty(s2) ' True In C : string s1 = null; string s2 = ; Console. Write Line(s1 = null / True Console. Write Line(s2 = null / False Console. Write Line(s1 = / False Console. Write Line(s2 = / True Console. Write Line(string. Is Null Or Empty(s1 / True Console. Write Line(string. Is Null Or Empty(s2 / True I wasn't quite expecting that. It appears that VB. Net treats an Nothing as an empty string. My guess is for compatibility with older versions of VB. This reinforces all the more that you should be using String. Is Null Or Empty for these sorts of checks, as it is more explicit what you are checking for, and works as expected.
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