String.IsNullOrEmpty(String) Method
Definition
Important
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Indicates whether the specified string is null
or an empty string ("").
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
- value
- String
The string to test.
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
.
using namespace System;
String^ Test( String^ s )
{
if (String::IsNullOrEmpty(s))
return "is null or empty";
else
return String::Format( "(\"{0}\") is neither null nor empty", s );
}
int main()
{
String^ s1 = "abcd";
String^ s2 = "";
String^ s3 = nullptr;
Console::WriteLine( "String s1 {0}.", Test( s1 ) );
Console::WriteLine( "String s2 {0}.", Test( s2 ) );
Console::WriteLine( "String s3 {0}.", 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.
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:
result = s == nullptr || s == String::Empty;
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.
using namespace System;
void main()
{
String^ s;
Console::WriteLine("The value of the string is '{0}'", s);
try {
Console::WriteLine("String length is {0}", 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.
String s = null;
Console.WriteLine("The value of the string is '{0}'", s);
try
{
Console.WriteLine("String length is {0}", 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 Main()
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 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::WriteLine("The length of '{0}' is {1}.", s, s->Length);
// The example displays the following output:
// The length of '' is 0.
String s = "";
Console.WriteLine("The length of '{0}' is {1}.", s, 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.