String.IsNullOrEmpty(String) Method

public:
 static bool IsNullOrEmpty(System::String ^ value);

public static bool IsNullOrEmpty(string value);

public static bool IsNullOrEmpty(string? value);

static member IsNullOrEmpty : string -> bool

Public Shared Function IsNullOrEmpty (value As String) As Boolean

Parameters

Returns

true if the value parameter is null or an empty string (""); otherwise, false.

Examples

The following example examines three strings and determines whether each string has a value, is an empty string, or is null.

string s1 = "abcd";
string s2 = "";
string s3 = null;

Console.WriteLine("String s1 {0}.", Test(s1));
Console.WriteLine("String s2 {0}.", Test(s2));
Console.WriteLine("String s3 {0}.", Test(s3));

String Test(string s)
{
if (String.IsNullOrEmpty(s))
 return "is null or empty";
else
 return String.Format("(\"{0}\") is neither null nor empty", s);
}

// The example displays the following output:
// String s1 ("abcd") is neither null nor empty.
// String s2 is null or empty.
// String s3 is null or empty.

Class Sample
 Public Shared Sub Main()
 Dim s1 As String = "abcd"
 Dim s2 As String = ""
 Dim s3 As String = Nothing
 
 Console.WriteLine("String s1 {0}.", Test(s1))
 Console.WriteLine("String s2 {0}.", Test(s2))
 Console.WriteLine("String s3 {0}.", Test(s3))
 End Sub
 
 Public Shared Function Test(s As String) As String
 If String.IsNullOrEmpty(s) Then
 Return "is null or empty"
 Else
 Return String.Format("(""{0}"") is neither null nor empty", s)
 End If
 End Function 
End Class 
' The example displays the following output:
' String s1 ("abcd") is neither null nor empty.
' String s2 is null or empty.
' String s3 is null or empty.

let test (s: string): string =
 if String.IsNullOrEmpty(s)
 then "is null or empty"
 else $"(\"{s}\") is neither null nor empty"

let s1 = "abcd"
let s2 = ""
let s3 = null

printfn "String s1 %s" (test s1)
printfn "String s2 %s" (test s2)
printfn "String s2 %s" (test s3)

// The example displays the following output:
// String s1 ("abcd") is neither null nor empty.
// String s2 is null or empty.
// String s3 is null or empty.

Remarks

IsNullOrEmpty is a convenience method that enables you to simultaneously test whether a String is null or its value is String.Empty. It is equivalent to the following code:

bool TestForNullOrEmpty(string s)
{
 bool result;
 result = s == null || s == string.Empty;
 return result;
}

string s1 = null;
string s2 = "";
Console.WriteLine(TestForNullOrEmpty(s1));
Console.WriteLine(TestForNullOrEmpty(s2));

// The example displays the following output:
// True
// True

result = s Is Nothing OrElse s = String.Empty

let testForNullOrEmpty (s: string): bool =
 s = null || s = String.Empty

let s1 = null
let s2 = ""

printfn "%b" (testForNullOrEmpty s1)
printfn "%b" (testForNullOrEmpty s2)

// The example displays the following output:
// true
// true

You can use the IsNullOrWhiteSpace method to test whether a string is null, its value is String.Empty, or it consists only of white-space characters.

What is a null string?

A string is null if it has not been assigned a value (in C++ and Visual Basic) or if it 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 NullReferenceException.

 String s = null;

 Console.WriteLine($"The value of the string is '{s}'");

 try 
 {
 Console.WriteLine($"String length is {s.Length}");
 }
 catch (NullReferenceException e) 
 {
 Console.WriteLine(e.Message);
 }

 // The example displays the following output:
 // The value of the string is ''
 // Object reference not set to an instance of an object.

Module Example
 Public Sub Main3()
 Dim s As String

 Console.WriteLine("The value of the string is '{0}'", s)

 Try
 Console.WriteLine("String length is {0}", s.Length)
 Catch e As NullReferenceException
 Console.WriteLine(e.Message)
 End Try
 End Sub
End Module
' The example displays the following output:
' The value of the string is ''
' Object reference not set to an instance of an object.

let (s: string) = null

printfn "The value of the string is '%s'" s

try
 printfn "String length is %d" s.Length
with
 | :? NullReferenceException as ex -> printfn "%s" ex.Message

// The example displays the following output:
// The value of the string is ''
// Object reference not set to an instance of an object.

What is an empty string?

A string is empty if it's 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.WriteLine($"The length of '{s}' is {s.Length}.");

// The example displays the following output:
// The length of '' is 0.

Dim s As String = ""
Console.WriteLine("The length of '{0}' is {1}.", s, s.Length)
' The example displays the following output:
' The length of '' is 0.

let s = ""
printfn "The length of '%s' is %d." s s.Length

// The example displays the following output:
// The length of '' is 0.

See also

• IsNullOrWhiteSpace(String)