# String.IsNullOrEmpty(String) Méthode

## Définition

Indique si la chaîne spécifiée est `null` ou une chaîne vide ("").Indicates whether the specified string is `null` or an empty string ("").

``````public:
static bool IsNullOrEmpty(System::String ^ value);``````
``public static bool IsNullOrEmpty (string value);``
``static member IsNullOrEmpty : string -> bool``
``Public Shared Function IsNullOrEmpty (value As String) As Boolean``

#### Paramètres

value
String

Chaîne à tester.The string to test.

#### Retours

`true` si le paramètre `value` est `null` ou une chaîne vide ("") ; sinon, `false`.`true` if the `value` parameter is `null` or an empty string (""); otherwise, `false`.

## Exemples

L’exemple suivant examine trois chaînes et détermine si chaque chaîne a une valeur, si est une chaîne vide ou si elle est `null`.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.
``````

## Remarques

IsNullOrEmpty est une méthode pratique qui vous permet de tester simultanément si un String est `null` ou si sa valeur est String.Empty.IsNullOrEmpty is a convenience method that enables you to simultaneously test whether a String is `null` or its value is String.Empty. Elle est équivalente au code suivant :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
``````

Vous pouvez utiliser la méthode IsNullOrWhiteSpace pour tester si une chaîne est `null`, si sa valeur est String.Emptyou si elle se compose uniquement d’espaces blancs.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.

### Qu’est-ce qu’une chaîne null ?What is a null string?

Une chaîne est `null` si aucune valeur n’a été assignée ( C++ dans et Visual Basic) ou si une valeur de `null`a été explicitement assignée.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`. Bien que la fonctionnalité de mise en forme composite puisse gérer gracieusement une chaîne NULL, comme le montre l’exemple suivant, en tentant d’en appeler une si ses membres lèvent une NullReferenceException.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.
``````

### Qu’est-ce qu’une chaîne vide ?What is an empty string?

Une chaîne est vide si une chaîne vide ("") ou String.Emptyest assignée explicitement.A string is empty if it is explicitly assigned an empty string ("") or String.Empty. Une chaîne vide a une Length de 0.An empty string has a Length of 0. L’exemple suivant crée une chaîne vide et affiche sa valeur et sa longueur.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.
``````