String.IsNullOrEmpty(String) String.IsNullOrEmpty(String) String.IsNullOrEmpty(String) String.IsNullOrEmpty(String) Method

定義

指定された文字列が null または空の文字列 ("") であるかどうかを示します。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

パラメーター

value
String String String String

テストする文字列。The string to test.

戻り値

true パラメーターが value または空の文字列 ("") の場合は null。それ以外の場合は falsetrue if the value parameter is null or an empty string (""); otherwise, false.

次の例は、3 つの文字列を検査し、各文字列の値を持つ、空の文字列、されるかを決定nullします。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.
using System;

class Sample 
{
    public static void Main() 
    {
    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));
    }

    public static 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.

注釈

IsNullOrEmpty 同時にテストすることができる便利なメソッドは、かどうかをStringnullまたはその値がString.Emptyします。IsNullOrEmpty is a convenience method that enables you to simultaneously test whether a String is null or its value is String.Empty. これは、次のコードに相当します。It is equivalent to the following code:

result = s == nullptr || s == String::Empty;
result = s == null || s == string.Empty;
result = s Is Nothing OrElse s = String.Empty

使用することができます、IsNullOrWhiteSpace文字列があるかどうかをテストするメソッドnull、その値はString.Empty、またはの空白文字だけで構成されます。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.

Null 文字列とは何ですか。What is a null string?

文字列がnull(C++ および Visual Basic) の値を割り当てられていない場合、または値の割り当てられて明示的にnullします。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. ただし、複合書式指定機能は次の例は、そのメンバーがスローされた場合は、いずれかを呼び出しますしようと null 文字列では、適切に処理をNullReferenceExceptionします。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.
using System;

public class Example
{
   public static void Main()
   {
      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.

空の文字列とは何ですか。What is an empty string?

文字列が空の文字列を明示的に割り当てられている場合は空 ("") またはString.Emptyします。A string is empty if it is explicitly assigned an empty string ("") or String.Empty. 空の文字列が、 Length 0 です。An empty string has a Length of 0. 次の例では、空の文字列を作成し、その値とその長さが表示されます。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.      

適用対象

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