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));
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 nulla 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.      

S’applique à

Voir aussi