Convert.ToDouble メソッド (String)

指定した String 形式の数値を、それと等価な倍精度浮動小数点数に変換します。

Overloads Public Shared Function ToDouble( _
   ByVal value As String _) As Double
[C#]
public static double ToDouble(stringvalue);
[C++]
public: static double ToDouble(String* value);
[JScript]
public static function ToDouble(
   value : String) : double;

パラメータ

• value
  変換する数値を格納している String 。

戻り値

value の値と等価な倍精度浮動小数点数。

または

value が null 参照 (Visual Basic では Nothing) の場合は 0。

例外

解説

戻り値は、value に対して Double.Parse メソッドを呼び出した結果得られる値です。

使用例

[Visual Basic, C#, C++] ToDouble を使用して、 String の値を Double の値に変換する方法については、次のコード例を参照してください。

 
Public Sub CovertDoubleFloat(ByVal doubleVal As Double)
    Dim singleVal As Single = 0

    ' Double to Single conversion can overflow.
    Try
        singleVal = System.Convert.ToSingle(doubleVal)
        System.Console.WriteLine("{0} as a Single is {1}", _
                                  doubleVal, singleVal)
    Catch exception As System.OverflowException
        System.Console.WriteLine( _
            "Overflow in Double-to-Float conversion.")
    End Try

    ' Conversion from Single to Double cannot overflow.
    doubleVal = System.Convert.ToDouble(singleVal)
    System.Console.WriteLine("{0} as a Double is: {1}", _
                              singleVal, doubleVal)
End Sub
    . . . 
Public Sub ConvertDoubleString(ByVal doubleVal As Double)

    Dim stringVal As String

    ' A conversion from Double to String cannot overflow.       
    stringVal = System.Convert.ToString(doubleVal)
    System.Console.WriteLine("{0} as a String is: {1}", _
                              doubleVal, stringVal)

    Try
        doubleVal = System.Convert.ToDouble(stringVal)
        System.Console.WriteLine("{0} as a Double is: {1}", _
                                  stringVal, doubleVal)
    Catch exception As System.OverflowException
        System.Console.WriteLine( _
            "Overflow in String-to-Double conversion.")
    Catch exception As System.FormatException
        System.Console.WriteLine( _
            "The string is not formatted as a Double.")
    Catch exception As System.ArgumentException
        System.Console.WriteLine("The string is null.")
    End Try

End Sub

[C#] 
public void CovertDoubleFloat(double doubleVal) {    
    float floatVal = 0;

    // Double to float conversion can overflow.
    try {
        floatVal = System.Convert.ToSingle(doubleVal);
        System.Console.WriteLine("{0} as a float is {1}",
            doubleVal, floatVal);
    } 
    catch (System.OverflowException) {
        System.Console.WriteLine(
            "Overflow in double-to-float conversion.");
    }

    // Conversion from float to double cannot overflow.
    doubleVal = System.Convert.ToDouble(floatVal);
    System.Console.WriteLine("{0} as a double is: {1}",
        floatVal, doubleVal);
}
    . . . 
public void ConvertDoubleString(double doubleVal) {
    
    string    stringVal;     

    // A conversion from Double to string cannot overflow.       
    stringVal = System.Convert.ToString(doubleVal);
    System.Console.WriteLine("{0} as a string is: {1}",
        doubleVal, stringVal);

    try {
        doubleVal = System.Convert.ToDouble(stringVal);
        System.Console.WriteLine("{0} as a double is: {1}",
            stringVal, doubleVal);
    } 
    catch (System.OverflowException) {
        System.Console.WriteLine(
            "Conversion from string-to-double overflowed.");
    }
    catch (System.FormatException) {
        System.Console.WriteLine(
            "The string was not formatted as a double.");
    }
    catch (System.ArgumentException) {
        System.Console.WriteLine(
            "The string pointed to null.");
    }
}

[C++] 

   void CovertDoubleFloat(double doubleVal)
   {    
      float floatVal = 0;

      // Double to float conversion can overflow.
      try {
         floatVal = System::Convert::ToSingle(doubleVal);
         System::Console::WriteLine(S" {0} as a float is {1}",
            __box(doubleVal), __box(floatVal));
      } catch (System::OverflowException*) {
         System::Console::WriteLine(S"Overflow in double-to-float conversion.");
      }

      // Conversion from float to double cannot overflow.
      doubleVal = System::Convert::ToDouble(floatVal);
      System::Console::WriteLine(S" {0} as a double is: {1}",
         __box(floatVal), __box(doubleVal));
   }
    . . . 

   void ConvertDoubleString(double doubleVal)
   {
      String*    stringVal;     

      // A conversion from Double to String* cannot overflow.       
      stringVal = System::Convert::ToString(doubleVal);
      System::Console::WriteLine(S" {0} as a String* is: {1}",
         __box(doubleVal), stringVal);

      try {
         doubleVal = System::Convert::ToDouble(stringVal);
         System::Console::WriteLine(S" {0} as a double is: {1}",
            stringVal, __box(doubleVal));
      } catch (System::OverflowException*) {
         System::Console::WriteLine(S"Conversion from String*-to-double overflowed.");
      } catch (System::FormatException*) {
         System::Console::WriteLine(S"The String* was not formatted as a double.");
      } catch (System::ArgumentException*) {
         System::Console::WriteLine(S"The String* pointed to null.");
      }
   }

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必要条件

プラットフォーム: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 ファミリ, .NET Compact Framework - Windows CE .NET, Common Language Infrastructure (CLI) Standard

参照

Convert クラス | Convert メンバ | System 名前空間 | Convert.ToDouble オーバーロードの一覧