Double Double Double Double Struct

定義

表示雙精度浮點數。Represents a double-precision floating-point number.

public value class Double : IComparable, IComparable<double>, IConvertible, IEquatable<double>, IFormattable
[System.Runtime.InteropServices.ComVisible(true)]
[System.Serializable]
public struct Double : IComparable, IComparable<double>, IConvertible, IEquatable<double>, IFormattable
type double = struct
    interface IFormattable
    interface IConvertible
Public Structure Double
Implements IComparable, IComparable(Of Double), IConvertible, IEquatable(Of Double), IFormattable
繼承
屬性
實作

範例

下列程式碼範例示範如何將Double:The following code example illustrates the use of Double:

// The Temperature class stores the temperature as a Double
// and delegates most of the functionality to the Double 
// implementation.
public ref class Temperature: public IComparable, public IFormattable
{
   // IComparable.CompareTo implementation.
public:
   virtual int CompareTo( Object^ obj )
   {
      if (obj == nullptr) return 1;
      
      if (dynamic_cast<Temperature^>(obj) )
      {
         Temperature^ temp = (Temperature^)(obj);
         return m_value.CompareTo( temp->m_value );
      }
      throw gcnew ArgumentException( "object is not a Temperature" );
   }

   // IFormattable.ToString implementation.
   virtual String^ ToString( String^ format, IFormatProvider^ provider )
   {
      if ( format != nullptr )
      {
         if ( format->Equals( "F" ) )
         {
            return String::Format( "{0}'F", this->Value.ToString() );
         }

         if ( format->Equals( "C" ) )
         {
            return String::Format( "{0}'C", this->Celsius.ToString() );
         }
      }
      return m_value.ToString( format, provider );
   }

   // Parses the temperature from a string in the form
   // [ws][sign]digits['F|'C][ws]
   static Temperature^ Parse( String^ s, NumberStyles styles, IFormatProvider^ provider )
   {
      Temperature^ temp = gcnew Temperature;

      if ( s->TrimEnd(nullptr)->EndsWith( "'F" ) )
      {
         temp->Value = Double::Parse( s->Remove( s->LastIndexOf( '\'' ), 2 ), styles, provider );
      }
      else
      if ( s->TrimEnd(nullptr)->EndsWith( "'C" ) )
      {
         temp->Celsius = Double::Parse( s->Remove( s->LastIndexOf( '\'' ), 2 ), styles, provider );
      }
      else
      {
         temp->Value = Double::Parse( s, styles, provider );
      }
      return temp;
   }

protected:
   double m_value;

public:
   property double Value 
   {
      double get()
      {
         return m_value;
      }

      void set( double value )
      {
         m_value = value;
      }
   }

   property double Celsius 
   {
      double get()
      {
         return (m_value - 32.0) / 1.8;
      }

      void set( double value )
      {
         m_value = 1.8 * value + 32.0;
      }
   }
};
// The Temperature class stores the temperature as a Double
// and delegates most of the functionality to the Double
// implementation.
public class Temperature : IComparable, IFormattable 
   {
	// IComparable.CompareTo implementation.
	public int CompareTo(object obj) {
           if (obj == null) return 1;
           
		Temperature temp = obj as Temperature;
           if (obj != null) 
			return m_value.CompareTo(temp.m_value);
		else
    			throw new ArgumentException("object is not a Temperature");	
	}

	// IFormattable.ToString implementation.
	public string ToString(string format, IFormatProvider provider) {
		if( format != null ) {
			if( format.Equals("F") ) {
				return String.Format("{0}'F", this.Value.ToString());
			}
			if( format.Equals("C") ) {
				return String.Format("{0}'C", this.Celsius.ToString());
			}
		}

		return m_value.ToString(format, provider);
	}

	// Parses the temperature from a string in the form
	// [ws][sign]digits['F|'C][ws]
	public static Temperature Parse(string s, NumberStyles styles, IFormatProvider provider) {
		Temperature temp = new Temperature();

		if( s.TrimEnd(null).EndsWith("'F") ) {
			temp.Value = Double.Parse( s.Remove(s.LastIndexOf('\''), 2), styles, provider);
		}
		else if( s.TrimEnd(null).EndsWith("'C") ) {
			temp.Celsius = Double.Parse( s.Remove(s.LastIndexOf('\''), 2), styles, provider);
		}
		else {
			temp.Value = Double.Parse(s, styles, provider);
		}

		return temp;
	}

	// The value holder
	protected double m_value;

	public double Value {
		get {
			return m_value;
		}
		set {
			m_value = value;
		}
	}

	public double Celsius {
		get {
			return (m_value-32.0)/1.8;
		}
		set {
			m_value = 1.8*value+32.0;
		}
	}
}
' Temperature class stores the value as Double
' and delegates most of the functionality 
' to the Double implementation.
Public Class Temperature
    Implements IComparable, IFormattable

    Public Overloads Function CompareTo(ByVal obj As Object) As Integer _
        Implements IComparable.CompareTo

        If TypeOf obj Is Temperature Then
            Dim temp As Temperature = CType(obj, Temperature)

            Return m_value.CompareTo(temp.m_value)
        End If

        Throw New ArgumentException("object is not a Temperature")
    End Function

    Public Overloads Function ToString(ByVal format As String, ByVal provider As IFormatProvider) As String _
        Implements IFormattable.ToString

        If Not (format Is Nothing) Then
            If format.Equals("F") Then
                Return [String].Format("{0}'F", Me.Value.ToString())
            End If
            If format.Equals("C") Then
                Return [String].Format("{0}'C", Me.Celsius.ToString())
            End If
        End If

        Return m_value.ToString(format, provider)
    End Function

    ' Parses the temperature from a string in form
    ' [ws][sign]digits['F|'C][ws]
    Public Shared Function Parse(ByVal s As String, ByVal styles As NumberStyles, ByVal provider As IFormatProvider) As Temperature
        Dim temp As New Temperature()

        If s.TrimEnd(Nothing).EndsWith("'F") Then
            temp.Value = Double.Parse(s.Remove(s.LastIndexOf("'"c), 2), styles, provider)
        Else
            If s.TrimEnd(Nothing).EndsWith("'C") Then
                temp.Celsius = Double.Parse(s.Remove(s.LastIndexOf("'"c), 2), styles, provider)
            Else
                temp.Value = Double.Parse(s, styles, provider)
            End If
        End If
        Return temp
    End Function

    ' The value holder
    Protected m_value As Double

    Public Property Value() As Double
        Get
            Return m_value
        End Get
        Set(ByVal Value As Double)
            m_value = Value
        End Set
    End Property

    Public Property Celsius() As Double
        Get
            Return (m_value - 32) / 1.8
        End Get
        Set(ByVal Value As Double)
            m_value = Value * 1.8 + 32
        End Set
    End Property
End Class

備註

Double實值型別代表值範圍從負 1.79769313486232e308 到正 1.79769313486232 e 308,以及正或負 0、 雙精確度 64 位元數字PositiveInfinityNegativeInfinity,並不是數字 (NaN).The Double value type represents a double-precision 64-bit number with values ranging from negative 1.79769313486232e308 to positive 1.79769313486232e308, as well as positive or negative zero, PositiveInfinity, NegativeInfinity, and not a number (NaN). 它用來代表值,是極大 (例如行星或個之間的距離) 或極小 (在公斤物質分子大量),通常並不精確 (例如距離地球另一個太陽系),Double類型符合 IEC 60559:1989 (IEEE 754) 二進位浮點運算的標準。It is intended to represent values that are extremely large (such as distances between planets or galaxies) or extremely small (the molecular mass of a substance in kilograms) and that often are imprecise (such as the distance from earth to another solar system), The Double type complies with the IEC 60559:1989 (IEEE 754) standard for binary floating-point arithmetic.

本主題包含下列章節:This topic consists of the following sections:

浮點數表示和有效位數Floating-Point Representation and Precision

Double資料型別雙精確度浮點值 64 位元二進位格式儲存下, 表所示:The Double data type stores double-precision floating-point values in a 64-bit binary format, as shown in the following table:

組件Part BitsBits
有效數字或尾數Significand or mantissa 0-510-51
指數Exponent 52-6252-62
符號 (0 = 正數、 1 = 負)Sign (0 = Positive, 1 = Negative) 6363

如同小數無法精確地表示有些小數值 (例如 1/3 或Math.PI),二進位分數是無法代表某些小數的值。Just as decimal fractions are unable to precisely represent some fractional values (such as 1/3 or Math.PI), binary fractions are unable to represent some fractional values. 例如,1/10,精確地由.1 以小數表示,被以.001100110011 為二進位分數,使用模式"0011"重複為無限大。For example, 1/10, which is represented precisely by .1 as a decimal fraction, is represented by .001100110011 as a binary fraction, with the pattern "0011" repeating to infinity. 在此情況下,浮點值會提供它所代表的數字不精確表示法。In this case, the floating-point value provides an imprecise representation of the number that it represents. 經常執行額外的數學運算的原始浮點數的值通常會提高其缺乏精確度。Performing additional mathematical operations on the original floating-point value often tends to increase its lack of precision. 比方說,如果我們比較結果乘以.1 10 新增.1 到.1 九次,我們會看到加入,因為它已牽涉到八個更多的作業,已產生較不精確的結果。For example, if we compare the result of multiplying .1 by 10 and adding .1 to .1 nine times, we see that addition, because it has involved eight more operations, has produced the less precise result. 請注意,此差異是只有當我們顯示兩個明顯Double使用"R"的值標準數值格式字串,如果需要,將會顯示所有 17 位數支援Double型別。Note that this disparity is apparent only if we display the two Double values by using the "R" standard numeric format string, which if necessary displays all 17 digits of precision supported by the Double type.

using System;

public class Example
{
   public static void Main()
   {
      Double value = .1;
      Double result1 = value * 10;
      Double result2 = 0;
      for (int ctr = 1; ctr <= 10; ctr++)
         result2 += value;

      Console.WriteLine(".1 * 10:           {0:R}", result1);
      Console.WriteLine(".1 Added 10 times: {0:R}", result2);
   }
}
// The example displays the following output:
//       .1 * 10:           1
//       .1 Added 10 times: 0.99999999999999989
Module Example
   Public Sub Main()
      Dim value As Double = .1
      Dim result1 As Double = value * 10
      Dim result2 As Double
      For ctr As Integer = 1 To 10
         result2 += value
      Next
      Console.WriteLine(".1 * 10:           {0:R}", result1)
      Console.WriteLine(".1 Added 10 times: {0:R}", result2)
   End Sub
End Module
' The example displays the following output:
'       .1 * 10:           1
'       .1 Added 10 times: 0.99999999999999989

因為小的二進位數值無法完全代表一些數字,浮點數可以只近似實際數字。Because some numbers cannot be represented exactly as fractional binary values, floating-point numbers can only approximate real numbers.

所有的浮點數也會有有限的數目的有效位數,其中也會決定如何精確的浮點值接近實際數字。All floating-point numbers also have a limited number of significant digits, which also determines how accurately a floating-point value approximates a real number. ADouble值具有最多 15 個有效小數位數,雖然內部維護最多 17 個位數。A Double value has up to 15 decimal digits of precision, although a maximum of 17 digits is maintained internally. 這表示某些浮點運算可能缺少有效位數變更為浮點值。This means that some floating-point operations may lack the precision to change a floating point value. 下列範例提供一個實例。The following example provides an illustration. 它定義非常大的浮點值,並將新增的產品Double.Epsilon和它的其中一個大關。It defines a very large floating-point value, and then adds the product of Double.Epsilon and one quadrillion to it. 不過,「 產品 」 是太小,無法修改原始的浮點值。The product, however, is too small to modify the original floating-point value. 其最小顯著性數字是千分之一秒,而中產品的最高有效位數是 10-309Its least significant digit is thousandths, whereas the most significant digit in the product is 10-309.

using System;

public class Example
{
   public static void Main()
   {
      Double value = 123456789012.34567;
      Double additional = Double.Epsilon * 1e15;
      Console.WriteLine("{0} + {1} = {2}", value, additional, 
                                           value + additional);
   }
}
// The example displays the following output:
//    123456789012.346 + 4.94065645841247E-309 = 123456789012.346
Module Example
   Public Sub Main()
      Dim value As Double = 123456789012.34567
      Dim additional As Double = Double.Epsilon * 1e15
      Console.WriteLine("{0} + {1} = {2}", value, additional, 
                                           value + additional)
   End Sub
End Module
' The example displays the following output:
'   123456789012.346 + 4.94065645841247E-309 = 123456789012.346

浮點數限制有效位數有數個結果:The limited precision of a floating-point number has several consequences:

  • 因為其最小有效位數不同,會出現特定的有效位數相等的兩個浮點數可能不比較相等。Two floating-point numbers that appear equal for a particular precision might not compare equal because their least significant digits are different. 在下列範例中,一系列數字加在一起,,以及其總計相較於其預期的總和。In the following example, a series of numbers are added together, and their total is compared with their expected total. 雖然兩個值會出現相同,呼叫Equals方法表示它們不是。Although the two values appear to be the same, a call to the Equals method indicates that they are not.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          Double[] values = { 10.0, 2.88, 2.88, 2.88, 9.0 };
          Double result = 27.64;
          Double total = 0;
          foreach (var value in values)
             total += value;
    
          if (total.Equals(result))
             Console.WriteLine("The sum of the values equals the total.");
          else
             Console.WriteLine("The sum of the values ({0}) does not equal the total ({1}).",
                               total, result); 
       }
    }
    // The example displays the following output:
    //      The sum of the values (36.64) does not equal the total (36.64).   
    //
    // If the index items in the Console.WriteLine statement are changed to {0:R},
    // the example displays the following output:
    //       The sum of the values (27.639999999999997) does not equal the total (27.64).   
    
    Module Example
       Public Sub Main()
          Dim values() As Double = { 10.0, 2.88, 2.88, 2.88, 9.0 }
          Dim result As Double = 27.64
          Dim total As Double
          For Each value In values
             total += value
          Next
          If total.Equals(result) Then
             Console.WriteLine("The sum of the values equals the total.")
          Else
             Console.WriteLine("The sum of the values ({0}) does not equal the total ({1}).",
                               total, result) 
          End If     
       End Sub
    End Module
    ' The example displays the following output:
    '      The sum of the values (36.64) does not equal the total (36.64).   
    '
    ' If the index items in the Console.WriteLine statement are changed to {0:R},
    ' the example displays the following output:
    '       The sum of the values (27.639999999999997) does not equal the total (27.64).   
    

    如果您變更中的格式項目Console.WriteLine(String, Object, Object)陳述式,從{0}{1}{0:R}{1:R}以顯示所有的有效位數,兩個Double很清楚兩個值相等的值,因為失去了在加法作業期間的有效位數。If you change the format items in the Console.WriteLine(String, Object, Object) statement from {0} and {1} to {0:R} and {1:R} to display all significant digits of the two Double values, it is clear that the two values are unequal because of a loss of precision during the addition operations. 在此情況下,解決問題,藉由呼叫Math.Round(Double, Int32)要捨入方法Double到所需的精確度,然後再執行比較的值。In this case, the issue can be resolved by calling the Math.Round(Double, Int32) method to round the Double values to the desired precision before performing the comparison.

  • 使用浮點數數學或比較運算可能不會產生相同的結果使用十進位數字時,如果因為二進位浮點數可能不等於的十進位數字。A mathematical or comparison operation that uses a floating-point number might not yield the same result if a decimal number is used, because the binary floating-point number might not equal the decimal number. 上述範例說明這顯示結果乘以.1 10,並加入.1 的時間。A previous example illustrated this by displaying the result of multiplying .1 by 10 and adding .1 times.

    當精確度與小數值的數字作業中很重要時,您可以使用Decimal而非Double型別。When accuracy in numeric operations with fractional values is important, you can use the Decimal rather than the Double type. 當數字的操作,具有超過範圍的整數值的精確度Int64UInt64型別是重要的是,使用BigInteger型別。When accuracy in numeric operations with integral values beyond the range of the Int64 or UInt64 types is important, use the BigInteger type.

  • 值可能不會反覆存取如果牽涉到浮點數。A value might not round-trip if a floating-point number is involved. 如果作業會將原始浮點數轉換成另一種形式,反運算將轉換回浮點數,轉換的形式,而且最終浮點數不等於原始值,即稱為反覆存取浮點數。A value is said to round-trip if an operation converts an original floating-point number to another form, an inverse operation transforms the converted form back to a floating-point number, and the final floating-point number is not equal to the original floating-point number. 來回行程可能會失敗,因為一或多個最低有效位數遺失或轉換變更。The round trip might fail because one or more least significant digits are lost or changed in a conversion. 在下列範例中,三個Double值被轉換成字串並儲存在檔案中。In the following example, three Double values are converted to strings and saved in a file. 如輸出所示,不過,即使值看起來相同,則還原的值不相等為原始值。As the output shows, however, even though the values appear to be identical, the restored values are not equal to the original values.

    using System;
    using System.IO;
    
    public class Example
    {
       public static void Main()
       {
          StreamWriter sw = new StreamWriter(@".\Doubles.dat");
          Double[] values = { 2.2/1.01, 1.0/3, Math.PI };
          for (int ctr = 0; ctr < values.Length; ctr++) {
             sw.Write(values[ctr].ToString());
             if (ctr != values.Length - 1)
                sw.Write("|");
          }      
          sw.Close();
          
          Double[] restoredValues = new Double[values.Length];
          StreamReader sr = new StreamReader(@".\Doubles.dat");
          string temp = sr.ReadToEnd();
          string[] tempStrings = temp.Split('|');
          for (int ctr = 0; ctr < tempStrings.Length; ctr++)
             restoredValues[ctr] = Double.Parse(tempStrings[ctr]);   
    
    
          for (int ctr = 0; ctr < values.Length; ctr++)
             Console.WriteLine("{0} {2} {1}", values[ctr], 
                               restoredValues[ctr],
                               values[ctr].Equals(restoredValues[ctr]) ? "=" : "<>");
       }
    }
    // The example displays the following output:
    //       2.17821782178218 <> 2.17821782178218
    //       0.333333333333333 <> 0.333333333333333
    //       3.14159265358979 <> 3.14159265358979
    
    Imports System.IO
    
    Module Example
       Public Sub Main()
          Dim sw As New StreamWriter(".\Doubles.dat")
          Dim values() As Double = { 2.2/1.01, 1.0/3, Math.PI }
          For ctr As Integer = 0 To values.Length - 1
             sw.Write(values(ctr).ToString())
             If ctr <> values.Length - 1 Then sw.Write("|")
          Next      
          sw.Close()
          
          Dim restoredValues(values.Length - 1) As Double
          Dim sr As New StreamReader(".\Doubles.dat")
          Dim temp As String = sr.ReadToEnd()
          Dim tempStrings() As String = temp.Split("|"c)
          For ctr As Integer = 0 To tempStrings.Length - 1
             restoredValues(ctr) = Double.Parse(tempStrings(ctr))   
          Next 
    
          For ctr As Integer = 0 To values.Length - 1
             Console.WriteLine("{0} {2} {1}", values(ctr), 
                               restoredValues(ctr),
                               If(values(ctr).Equals(restoredValues(ctr)), "=", "<>"))
          Next
       End Sub
    End Module
    ' The example displays the following output:
    '       2.17821782178218 <> 2.17821782178218
    '       0.333333333333333 <> 0.333333333333333
    '       3.14159265358979 <> 3.14159265358979
    

    在此情況下,值可以是成功的來回時間使用"G17"標準數值格式字串保留完整的有效位數的Double值,如下列範例所示。In this case, the values can be successfully round-tripped by using the "G17" standard numeric format string to preserve the full precision of Double values, as the following example shows.

    using System;
    using System.IO;
    
    public class Example
    {
       public static void Main()
       {
          StreamWriter sw = new StreamWriter(@".\Doubles.dat");
          Double[] values = { 2.2/1.01, 1.0/3, Math.PI };
          for (int ctr = 0; ctr < values.Length; ctr++) 
             sw.Write("{0:G17}{1}", values[ctr], ctr < values.Length - 1 ? "|" : "" );
    
          sw.Close();
          
          Double[] restoredValues = new Double[values.Length];
          StreamReader sr = new StreamReader(@".\Doubles.dat");
          string temp = sr.ReadToEnd();
          string[] tempStrings = temp.Split('|');
          for (int ctr = 0; ctr < tempStrings.Length; ctr++)
             restoredValues[ctr] = Double.Parse(tempStrings[ctr]);   
    
    
          for (int ctr = 0; ctr < values.Length; ctr++)
             Console.WriteLine("{0} {2} {1}", values[ctr], 
                               restoredValues[ctr],
                               values[ctr].Equals(restoredValues[ctr]) ? "=" : "<>");
       }
    }
    // The example displays the following output:
    //       2.17821782178218 = 2.17821782178218
    //       0.333333333333333 = 0.333333333333333
    //       3.14159265358979 = 3.14159265358979
    
    Imports System.IO
    
    Module Example
       Public Sub Main()
          Dim sw As New StreamWriter(".\Doubles.dat")
          Dim values() As Double = { 2.2/1.01, 1.0/3, Math.PI }
          For ctr As Integer = 0 To values.Length - 1
             sw.Write("{0:G17}{1}", values(ctr), 
                      If(ctr < values.Length - 1, "|", ""))
          Next      
          sw.Close()
          
          Dim restoredValues(values.Length - 1) As Double
          Dim sr As New StreamReader(".\Doubles.dat")
          Dim temp As String = sr.ReadToEnd()
          Dim tempStrings() As String = temp.Split("|"c)
          For ctr As Integer = 0 To tempStrings.Length - 1
             restoredValues(ctr) = Double.Parse(tempStrings(ctr))   
          Next 
    
          For ctr As Integer = 0 To values.Length - 1
             Console.WriteLine("{0} {2} {1}", values(ctr), 
                               restoredValues(ctr),
                               If(values(ctr).Equals(restoredValues(ctr)), "=", "<>"))
          Next
       End Sub
    End Module
    ' The example displays the following output:
    '       2.17821782178218 = 2.17821782178218
    '       0.333333333333333 = 0.333333333333333
    '       3.14159265358979 = 3.14159265358979
    

重要

當搭配Double值,"R"格式規範,在某些情況下無法成功地反覆存取原始值。When used with a Double value, the "R" format specifier in some cases fails to successfully round-trip the original value. 若要確定Double值成功地反覆存取,使用"G17"格式規範。To ensure that Double values successfully round-trip, use the "G17" format specifier.

  • Single 值有較少精確度卻高於Double值。Single values have less precision than Double values. ASingle值轉換成看似相當Double通常不等於Double因為有效位數的差異值。A Single value that is converted to a seemingly equivalent Double often does not equal the Double value because of differences in precision. 在下列範例中,相同的除法運算的結果指派給DoubleSingle值。In the following example, the result of identical division operations is assigned to a Double and a Single value. 在後Single的值轉換為Double,比較兩個值會顯示不相等。After the Single value is cast to a Double, a comparison of the two values shows that they are unequal.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          Double value1 = 1/3.0;
          Single sValue2 = 1/3.0f;
          Double value2 = (Double) sValue2;
          Console.WriteLine("{0:R} = {1:R}: {2}", value1, value2, 
                                              value1.Equals(value2));
       }
    }
    // The example displays the following output:
    //        0.33333333333333331 = 0.3333333432674408: False
    
    Module Example
       Public Sub Main()
          Dim value1 As Double = 1/3
          Dim sValue2 As Single = 1/3
          Dim value2 As Double = CDbl(sValue2)
          Console.WriteLine("{0} = {1}: {2}", value1, value2, value1.Equals(value2))
       End Sub
    End Module
    ' The example displays the following output:
    '       0.33333333333333331 = 0.3333333432674408: False
    

    若要避免這個問題,請使用Double代替Single資料類型或使用Round方法,讓這兩個值具有相同的有效位數。To avoid this problem, use either the Double in place of the Single data type, or use the Round method so that both values have the same precision.

此外,與算術和指派作業的結果Double值可能稍有不同的平台的有效位數遺失因為Double型別。In addition, the result of arithmetic and assignment operations with Double values may differ slightly by platform because of the loss of precision of the Double type. 例如,指派常值的結果Double值而異的 32 位元和 64 位元版本的.NET framework 中。For example, the result of assigning a literal Double value may differ in the 32-bit and 64-bit versions of the .NET Framework. 下列範例說明這點差異時常值-4.42330604244772E-305 和變數,其值為-4.42330604244772E-305 指派給Double變數。The following example illustrates this difference when the literal value -4.42330604244772E-305 and a variable whose value is -4.42330604244772E-305 are assigned to a Double variable. 請注意,結果Parse(String)方法在此情況下不會發生遺失有效位數。Note that the result of the Parse(String) method in this case does not suffer from a loss of precision.

double value = -4.42330604244772E-305;

double fromLiteral = -4.42330604244772E-305;
double fromVariable = value;
double fromParse = Double.Parse("-4.42330604244772E-305");

Console.WriteLine("Double value from literal: {0,29:R}", fromLiteral);
Console.WriteLine("Double value from variable: {0,28:R}", fromVariable);
Console.WriteLine("Double value from Parse method: {0,24:R}", fromParse);      
// On 32-bit versions of the .NET Framework, the output is:
//    Double value from literal:        -4.42330604244772E-305
//    Double value from variable:       -4.42330604244772E-305
//    Double value from Parse method:   -4.42330604244772E-305
//
// On other versions of the .NET Framework, the output is:
//    Double value from literal:      -4.4233060424477198E-305
//    Double value from variable:     -4.4233060424477198E-305
//    Double value from Parse method:   -4.42330604244772E-305      
Dim value As Double = -4.42330604244772E-305

Dim fromLiteral As Double = -4.42330604244772E-305
Dim fromVariable As Double = value
Dim fromParse As Double = Double.Parse("-4.42330604244772E-305")

Console.WriteLine("Double value from literal: {0,29:R}", fromLiteral)
Console.WriteLine("Double value from variable: {0,28:R}", fromVariable)
Console.WriteLine("Double value from Parse method: {0,24:R}", fromParse)      
' On 32-bit versions of the .NET Framework, the output is:
'    Double value from literal:        -4.42330604244772E-305
'    Double value from variable:       -4.42330604244772E-305
'    Double value from Parse method:   -4.42330604244772E-305
'
' On other versions of the .NET Framework, the output is:
'    Double value from literal:        -4.4233060424477198E-305
'    Double value from variable:       -4.4233060424477198E-305
'    Double value from Parse method:     -4.42330604244772E-305      

測試相等Testing for Equality

若要才會被視為相等,兩個Double值必須代表相同的值。To be considered equal, two Double values must represent identical values. 不過,因為在精確度值之間的差異,或因為遺失一或兩個值的有效位數,應該通常是相同的浮點值變得不相等因為其最小有效位數的差異。However, because of differences in precision between values, or because of a loss of precision by one or both values, floating-point values that are expected to be identical often turn out to be unequal because of differences in their least significant digits. 如此一來,呼叫Equals方法,以判斷兩個值是否相等或呼叫CompareTo方法,以判斷兩個之間的關聯性Double值,通常會產生非預期的結果。As a result, calls to the Equals method to determine whether two values are equal, or calls to the CompareTo method to determine the relationship between two Double values, often yield unexpected results. 這是出現在下列範例中,其中兩個明顯等於Double值變得不相等因為第一個有 15 個位數的精確度,第二個有 17。This is evident in the following example, where two apparently equal Double values turn out to be unequal because the first has 15 digits of precision, while the second has 17.

using System;

public class Example
{
   public static void Main()
   {
      double value1 = .333333333333333;
      double value2 = 1.0/3;
      Console.WriteLine("{0:R} = {1:R}: {2}", value1, value2, value1.Equals(value2));
   }
}
// The example displays the following output:
//        0.333333333333333 = 0.33333333333333331: False
Module Example
   Public Sub Main()
      Dim value1 As Double = .333333333333333
      Dim value2 As Double = 1/3
      Console.WriteLine("{0:R} = {1:R}: {2}", value1, value2, value1.Equals(value2))
   End Sub
End Module
' The example displays the following output:
'       0.333333333333333 = 0.33333333333333331: False

導出的值,通常當做不同的方式,遵循不同的程式碼路徑,並且證明不相等。Calculated values that follow different code paths and that are manipulated in different ways often prove to be unequal. 在下列範例中,一個Double平方值,並計算再還原為原始值的平方根。In the following example, one Double value is squared, and then the square root is calculated to restore the original value. 第二個Double會乘以 3.51 和平方之前 3.51 還原為原始值除以結果的平方根。A second Double is multiplied by 3.51 and squared before the square root of the result is divided by 3.51 to restore the original value. 雖然兩個值看起來相同,但呼叫Equals(Double)方法指出它們是否不相等。Although the two values appear to be identical, a call to the Equals(Double) method indicates that they are not equal. 傳回顯示的每個雙精度浮點數值的所有有效位數的結果字串中使用"R"標準格式字串會顯示第二個值是.0000000000001 第一個大於或等於。Using the "R" standard format string to return a result string that displays all the significant digits of each Double value shows that the second value is .0000000000001 less than the first.

using System;

public class Example
{
   public static void Main()
   {
      double value1 = 100.10142;
      value1 = Math.Sqrt(Math.Pow(value1, 2));
      double value2 = Math.Pow(value1 * 3.51, 2);
      value2 = Math.Sqrt(value2) / 3.51;
      Console.WriteLine("{0} = {1}: {2}\n", 
                        value1, value2, value1.Equals(value2)); 
      Console.WriteLine("{0:R} = {1:R}", value1, value2); 
   }
}
// The example displays the following output:
//    100.10142 = 100.10142: False
//    
//    100.10142 = 100.10141999999999
Module Example
   Public Sub Main()
      Dim value1 As Double = 100.10142
      value1 = Math.Sqrt(Math.Pow(value1, 2))
      Dim value2 As Double = Math.Pow(value1 * 3.51, 2)
      value2 = Math.Sqrt(value2) / 3.51
      Console.WriteLine("{0} = {1}: {2}", 
                        value1, value2, value1.Equals(value2)) 
      Console.WriteLine()
      Console.WriteLine("{0:R} = {1:R}", value1, value2) 
   End Sub
End Module
' The example displays the following output:
'    100.10142 = 100.10142: False
'    
'    100.10142 = 100.10141999999999

中的情況下遺失有效位數可能會影響比較的結果,您可以採用任何下列的替代方案,於呼叫EqualsCompareTo方法:In cases where a loss of precision is likely to affect the result of a comparison, you can adopt any of the following alternatives to calling the Equals or CompareTo method:

  • 呼叫Math.Round方法,以確保這兩個值都有相同的精確度。Call the Math.Round method to ensure that both values have the same precision. 下列範例會修改先前的範例,為使用這種方法,讓兩個小數值相等。The following example modifies a previous example to use this approach so that two fractional values are equivalent.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          double value1 = .333333333333333;
          double value2 = 1.0/3;
          int precision = 7;
          value1 = Math.Round(value1, precision);
          value2 = Math.Round(value2, precision);
          Console.WriteLine("{0:R} = {1:R}: {2}", value1, value2, value1.Equals(value2));
       }
    }
    // The example displays the following output:
    //        0.3333333 = 0.3333333: True
    
    Module Example
       Public Sub Main()
          Dim value1 As Double = .333333333333333
          Dim value2 As Double = 1/3
          Dim precision As Integer = 7
          value1 = Math.Round(value1, precision)
          value2 = Math.Round(value2, precision)
          Console.WriteLine("{0:R} = {1:R}: {2}", value1, value2, value1.Equals(value2))
       End Sub
    End Module
    ' The example displays the following output:
    '       0.3333333 = 0.3333333: True
    

    不過要注意的是,有效位數的問題,仍適用於的中點值捨入。Note, though, that the problem of precision still applies to rounding of midpoint values. 如需詳細資訊,請參閱 Math.Round(Double, Int32, MidpointRounding) 方法。For more information, see the Math.Round(Double, Int32, MidpointRounding) method.

  • 近似相等測試而不是等號比較。Test for approximate equality rather than equality. 這需要您定義的其中一個絕對數量的兩個值可以用不同,但仍視為相等,或您定義相對量的較小的值可以偏離較大的值。This requires that you define either an absolute amount by which the two values can differ but still be equal, or that you define a relative amount by which the smaller value can diverge from the larger value.

    警告

    Double.Epsilon 有時會作為兩個之間距離的絕對單位Double值時測試是否相等。Double.Epsilon is sometimes used as an absolute measure of the distance between two Double values when testing for equality. 不過,Double.Epsilon測量的最小的可能值,可以新增或減去,Double其值為零。However, Double.Epsilon measures the smallest possible value that can be added to, or subtracted from, a Double whose value is zero. 為大部分的正數和負數Double的值,而值Double.Epsilon太小而無法偵測到。For most positive and negative Double values, the value of Double.Epsilon is too small to be detected. 因此,除了為零的值,我們不建議在測試相等。Therefore, except for values that are zero, we do not recommend its use in tests for equality.

    下列範例會使用第二種方法來定義IsApproximatelyEqual方法,來測試兩個值之間的相對差異。The following example uses the latter approach to define an IsApproximatelyEqual method that tests the relative difference between two values. 它也會對照的呼叫結果IsApproximatelyEqual方法和Equals(Double)方法。It also contrasts the result of calls to the IsApproximatelyEqual method and the Equals(Double) method.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          double one1 = .1 * 10;
          double one2 = 0;
          for (int ctr = 1; ctr <= 10; ctr++)
             one2 += .1;
    
          Console.WriteLine("{0:R} = {1:R}: {2}", one1, one2, one1.Equals(one2));
          Console.WriteLine("{0:R} is approximately equal to {1:R}: {2}", 
                            one1, one2, 
                            IsApproximatelyEqual(one1, one2, .000000001));   
       }
    
       static bool IsApproximatelyEqual(double value1, double value2, double epsilon)
       {
          // If they are equal anyway, just return True.
          if (value1.Equals(value2))
             return true;
    
          // Handle NaN, Infinity.
          if (Double.IsInfinity(value1) | Double.IsNaN(value1))
             return value1.Equals(value2);
          else if (Double.IsInfinity(value2) | Double.IsNaN(value2))
             return value1.Equals(value2);
    
          // Handle zero to avoid division by zero
          double divisor = Math.Max(value1, value2);
          if (divisor.Equals(0)) 
             divisor = Math.Min(value1, value2);
          
          return Math.Abs(value1 - value2)/divisor <= epsilon;           
       } 
    }
    // The example displays the following output:
    //       1 = 0.99999999999999989: False
    //       1 is approximately equal to 0.99999999999999989: True
    
    Module Example
       Public Sub Main()
          Dim one1 As Double = .1 * 10
          Dim one2 As Double = 0
          For ctr As Integer = 1 To 10
             one2 += .1
          Next
          Console.WriteLine("{0:R} = {1:R}: {2}", one1, one2, one1.Equals(one2))
          Console.WriteLine("{0:R} is approximately equal to {1:R}: {2}", 
                            one1, one2, 
                            IsApproximatelyEqual(one1, one2, .000000001))   
       End Sub
    
       Function IsApproximatelyEqual(value1 As Double, value2 As Double, 
                                     epsilon As Double) As Boolean
          ' If they are equal anyway, just return True.
          If value1.Equals(value2) Then Return True
          
          ' Handle NaN, Infinity.
          If Double.IsInfinity(value1) Or Double.IsNaN(value1) Then
             Return value1.Equals(value2)
          Else If Double.IsInfinity(value2) Or Double.IsNaN(value2)
             Return value1.Equals(value2)
          End If
          
          ' Handle zero to avoid division by zero
          Dim divisor As Double = Math.Max(value1, value2)
          If divisor.Equals(0) Then
             divisor = Math.Min(value1, value2)
          End If 
          
          Return Math.Abs(value1 - value2)/divisor <= epsilon           
       End Function
    End Module
    ' The example displays the following output:
    '       1 = 0.99999999999999989: False
    '       1 is approximately equal to 0.99999999999999989: True
    

浮點值和例外狀況Floating-Point Values and Exceptions

不同於使用整數類資料類型,在溢位或不合法的作業,例如部門的情況下擲回例外狀況為零,作業具有浮點值的作業不擲回例外狀況。Unlike operations with integral types, which throw exceptions in cases of overflow or illegal operations such as division by zero, operations with floating-point values do not throw exceptions. 相反地,例外的情況下,在浮點運算的結果是零,正無限大、 負無限大或不是數字 (NaN):Instead, in exceptional situations, the result of a floating-point operation is zero, positive infinity, negative infinity, or not a number (NaN):

  • 如果浮點運算的結果太小,目的格式,則結果會是零。If the result of a floating-point operation is too small for the destination format, the result is zero. 這可能會乘以兩個非常小的數字,如下列範例所示。This can occur when two very small numbers are multiplied, as the following example shows.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          Double value1 = 1.1632875981534209e-225;
          Double value2 = 9.1642346778e-175;
          Double result = value1 * value2;
          Console.WriteLine("{0} * {1} = {2}", value1, value2, result);
          Console.WriteLine("{0} = 0: {1}", result, result.Equals(0.0));
       }
    }
    // The example displays the following output:
    //       1.16328759815342E-225 * 9.1642346778E-175 = 0
    //       0 = 0: True
    
    Module Example
       Public Sub Main()
          Dim value1 As Double = 1.1632875981534209e-225
          Dim value2 As Double = 9.1642346778e-175
          Dim result As Double = value1 * value2
          Console.WriteLine("{0} * {1} = {2}", value1, value2, result)
          Console.WriteLine("{0} = 0: {1}", result, result.Equals(0.0))
       End Sub
    End Module
    ' The example displays the following output:
    '       1.16328759815342E-225 * 9.1642346778E-175 = 0
    '       0 = 0: True
    
  • 浮點運算的結果大小超過目的格式的範圍,作業的結果是否PositiveInfinityNegativeInfinity視需要結果的正負號。If the magnitude of the result of a floating-point operation exceeds the range of the destination format, the result of the operation is PositiveInfinity or NegativeInfinity, as appropriate for the sign of the result. 溢位運算的結果Double.MaxValuePositiveInfinity,並造成溢位運算的結果Double.MinValueNegativeInfinity,如下列範例所示。The result of an operation that overflows Double.MaxValue is PositiveInfinity, and the result of an operation that overflows Double.MinValue is NegativeInfinity, as the following example shows.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          Double value1 = 4.565e153;
          Double value2 = 6.9375e172;
          Double result = value1 * value2;
          Console.WriteLine("PositiveInfinity: {0}", 
                             Double.IsPositiveInfinity(result));
          Console.WriteLine("NegativeInfinity: {0}\n", 
                            Double.IsNegativeInfinity(result));
    
          value1 = -value1;
          result = value1 * value2;
          Console.WriteLine("PositiveInfinity: {0}", 
                             Double.IsPositiveInfinity(result));
          Console.WriteLine("NegativeInfinity: {0}", 
                            Double.IsNegativeInfinity(result));
       }
    }                                                                 
    
    // The example displays the following output:
    //       PositiveInfinity: True
    //       NegativeInfinity: False
    //       
    //       PositiveInfinity: False
    //       NegativeInfinity: True
    
    Module Example
       Public Sub Main()
          Dim value1 As Double = 4.565e153
          Dim value2 As Double = 6.9375e172
          Dim result As Double = value1 * value2
          Console.WriteLine("PositiveInfinity: {0}", 
                             Double.IsPositiveInfinity(result))
          Console.WriteLine("NegativeInfinity: {0}", 
                            Double.IsNegativeInfinity(result))
          Console.WriteLine()                  
          value1 = -value1
          result = value1 * value2
          Console.WriteLine("PositiveInfinity: {0}", 
                             Double.IsPositiveInfinity(result))
          Console.WriteLine("NegativeInfinity: {0}", 
                            Double.IsNegativeInfinity(result))
       End Sub
    End Module
    ' The example displays the following output:
    '       PositiveInfinity: True
    '       NegativeInfinity: False
    '       
    '       PositiveInfinity: False
    '       NegativeInfinity: True
    

    PositiveInfinity 也產生除以零正值被除數,與和NegativeInfinity除法運算結果與負被除數為零。PositiveInfinity also results from a division by zero with a positive dividend, and NegativeInfinity results from a division by zero with a negative dividend.

  • 如果浮點運算無效,作業的結果是NaNIf a floating-point operation is invalid, the result of the operation is NaN. 比方說,NaN天時,下列作業:For example, NaN results from the following operations:

  • 與無效輸入任何浮點運算。Any floating-point operation with an invalid input. 例如,呼叫Math.Sqrt以負數值的方法會傳回NaN,如未呼叫Math.Acos值大於 1 或更少負一的方法。For example, calling the Math.Sqrt method with a negative value returns NaN, as does calling the Math.Acos method with a value that is greater than one or less than negative one.

  • 使用引數,其值的任何作業Double.NaNAny operation with an argument whose value is Double.NaN.

型別轉換和雙精確度結構Type conversions and the Double structure

Double結構並未定義任何明確或隱含的轉換運算子; 相反地,轉換會由編譯器實作。The Double structure does not define any explicit or implicit conversion operators; instead, conversions are implemented by the compiler.

轉換至任何基本數值類型的值Double是擴展轉換,因此不需要明確轉換運算子或呼叫轉換方法,除非編譯器明確需要。The conversion of the value of any primitive numeric type to a Double is a widening conversion and therefore does not require an explicit cast operator or call to a conversion method unless a compiler explicitly requires it. 例如,C# 編譯器轉換需要轉型運算子DecimalDouble,而 Visual Basic 編譯器並不會。For example, the C# compiler requires a casting operator for conversions from Decimal to Double, while the Visual Basic compiler does not. 下列範例會轉換至其他基本數值類型的最小值或最大值DoubleThe following example converts the minimum or maximum value of other primitive numeric types to a Double.

using System;

public class Example
{
   public static void Main()
   {
      dynamic[] values = { Byte.MinValue, Byte.MaxValue, Decimal.MinValue,
                           Decimal.MaxValue, Int16.MinValue, Int16.MaxValue,
                           Int32.MinValue, Int32.MaxValue, Int64.MinValue,
                           Int64.MaxValue, SByte.MinValue, SByte.MaxValue,
                           Single.MinValue, Single.MaxValue, UInt16.MinValue,
                           UInt16.MaxValue, UInt32.MinValue, UInt32.MaxValue,
                           UInt64.MinValue, UInt64.MaxValue };
      double dblValue;
      foreach (var value in values) {
         if (value.GetType() == typeof(Decimal))
            dblValue = (Double) value;
         else
            dblValue = value;
         Console.WriteLine("{0} ({1}) --> {2:R} ({3})",
                           value, value.GetType().Name,
                           dblValue, dblValue.GetType().Name);
      }
   }
}
// The example displays the following output:
//    0 (Byte) --> 0 (Double)
//    255 (Byte) --> 255 (Double)
//    -79228162514264337593543950335 (Decimal) --> -7.9228162514264338E+28 (Double)
//    79228162514264337593543950335 (Decimal) --> 7.9228162514264338E+28 (Double)
//    -32768 (Int16) --> -32768 (Double)
//    32767 (Int16) --> 32767 (Double)
//    -2147483648 (Int32) --> -2147483648 (Double)
//    2147483647 (Int32) --> 2147483647 (Double)
//    -9223372036854775808 (Int64) --> -9.2233720368547758E+18 (Double)
//    9223372036854775807 (Int64) --> 9.2233720368547758E+18 (Double)
//    -128 (SByte) --> -128 (Double)
//    127 (SByte) --> 127 (Double)
//    -3.402823E+38 (Single) --> -3.4028234663852886E+38 (Double)
//    3.402823E+38 (Single) --> 3.4028234663852886E+38 (Double)
//    0 (UInt16) --> 0 (Double)
//    65535 (UInt16) --> 65535 (Double)
//    0 (UInt32) --> 0 (Double)
//    4294967295 (UInt32) --> 4294967295 (Double)
//    0 (UInt64) --> 0 (Double)
//    18446744073709551615 (UInt64) --> 1.8446744073709552E+19 (Double)
Module Example
   Public Sub Main()
      Dim values() As Object = { Byte.MinValue, Byte.MaxValue, Decimal.MinValue,
                                 Decimal.MaxValue, Int16.MinValue, Int16.MaxValue,
                                 Int32.MinValue, Int32.MaxValue, Int64.MinValue,
                                 Int64.MaxValue, SByte.MinValue, SByte.MaxValue,
                                 Single.MinValue, Single.MaxValue, UInt16.MinValue,
                                 UInt16.MaxValue, UInt32.MinValue, UInt32.MaxValue,
                                 UInt64.MinValue, UInt64.MaxValue }
      Dim dblValue As Double
      For Each value In values
         dblValue = value
         Console.WriteLine("{0} ({1}) --> {2:R} ({3})",
                           value, value.GetType().Name,
                           dblValue, dblValue.GetType().Name)
      Next
   End Sub
End Module
' The example displays the following output:
'    0 (Byte) --> 0 (Double)
'    255 (Byte) --> 255 (Double)
'    -79228162514264337593543950335 (Decimal) --> -7.9228162514264338E+28 (Double)
'    79228162514264337593543950335 (Decimal) --> 7.9228162514264338E+28 (Double)
'    -32768 (Int16) --> -32768 (Double)
'    32767 (Int16) --> 32767 (Double)
'    -2147483648 (Int32) --> -2147483648 (Double)
'    2147483647 (Int32) --> 2147483647 (Double)
'    -9223372036854775808 (Int64) --> -9.2233720368547758E+18 (Double)
'    9223372036854775807 (Int64) --> 9.2233720368547758E+18 (Double)
'    -128 (SByte) --> -128 (Double)
'    127 (SByte) --> 127 (Double)
'    -3.402823E+38 (Single) --> -3.4028234663852886E+38 (Double)
'    3.402823E+38 (Single) --> 3.4028234663852886E+38 (Double)
'    0 (UInt16) --> 0 (Double)
'    65535 (UInt16) --> 65535 (Double)
'    0 (UInt32) --> 0 (Double)
'    4294967295 (UInt32) --> 4294967295 (Double)
'    0 (UInt64) --> 0 (Double)
'    18446744073709551615 (UInt64) --> 1.8446744073709552E+19 (Double)

颾魤 ㄛSingleSingle.NaNSingle.PositiveInfinity,以及Single.NegativeInfinity轉換到Double.NaNDouble.PositiveInfinity,和Double.NegativeInfinity分別。In addition, the Single values Single.NaN, Single.PositiveInfinity, and Single.NegativeInfinity covert to Double.NaN, Double.PositiveInfinity, and Double.NegativeInfinity, respectively.

請注意,某些數字型別,值的轉換Double值可能會涉及遺失有效位數。Note that the conversion of the value of some numeric types to a Double value can involve a loss of precision. 如範例所示,遺失有效位數時,可能轉換DecimalInt64Single,以及UInt64Double值。As the example illustrates, a loss of precision is possible when converting Decimal, Int64, Single, and UInt64 values to Double values.

轉換Double值與任何其他基本的數值資料類型的值是縮小轉換,而且需要轉換運算子 (在 C# 中)、 (在 Visual Basic) 的轉換方法或呼叫Convert方法。The conversion of a Double value to a value of any other primitive numeric data type is a narrowing conversion and requires a cast operator (in C#), a conversion method (in Visual Basic), or a call to a Convert method. 值超出範圍的目標資料類型,都由目標類型的定義MinValueMaxValue屬性,行為如下表所示。Values that are outside the range of the target data type, which are defined by the target type's MinValue and MaxValue properties, behave as shown in the following table.

目標類型Target type 結果Result
任何整數類資料類型Any integral type OverflowException轉換檢查的內容中發生的例外狀況。An OverflowException exception if the conversion occurs in a checked context.

如果在 unchecked 內容中 (C# 中的預設值),就會發生轉換,轉換作業成功,但值溢位。If the conversion occurs in an unchecked context (the default in C#), the conversion operation succeeds but the value overflows.
Decimal OverflowException 例外狀況。An OverflowException exception.
Single Single.NegativeInfinity 負數的值。Single.NegativeInfinity for negative values.

Single.PositiveInfinity 正數值。Single.PositiveInfinity for positive values.

颾魤 ㄛ Double.NaNDouble.PositiveInfinity,並Double.NegativeInfinity擲回OverflowExceptionchecked 的內容中,但這些值的溢位時轉換成在 unchecked 內容中的整數的整數的轉換。In addition, Double.NaN, Double.PositiveInfinity, and Double.NegativeInfinity throw an OverflowException for conversions to integers in a checked context, but these values overflow when converted to integers in an unchecked context. 轉換成Decimal,則一律會擲回OverflowExceptionFor conversions to Decimal, they always throw an OverflowException. 轉換成Single,它們會轉換成Single.NaNSingle.PositiveInfinity,和Single.NegativeInfinity分別。For conversions to Single, they convert to Single.NaN, Single.PositiveInfinity, and Single.NegativeInfinity, respectively.

請注意,遺失有效位數可能會使轉換Double成另一個數值類型的值。Note that a loss of precision may result from converting a Double value to another numeric type. 在將非整數的轉換的情況下Double值,如範例輸出所示,小數部分時遺失Double值四捨五入 (就像在 Visual Basic) 或截斷 (例如 C# 中)。In the case of converting non-integral Double values, as the output from the example shows, the fractional component is lost when the Double value is either rounded (as in Visual Basic) or truncated (as in C#). 轉換成DecimalSingle的值,Double值不能精確的表示法中的目標資料類型。For conversions to Decimal and Single values, the Double value may not have a precise representation in the target data type.

下列範例會將許多Double數個其他數值類型的值。The following example converts a number of Double values to several other numeric types. 在 Visual Basic (預設值),和在 C# 中檢查的內容中會發生轉換 (因為檢查關鍵字)。The conversions occur in a checked context in Visual Basic (the default) and in C# (because of the checked keyword). 此範例的輸出會顯示轉換的結果中這兩個核取核取的內容。The output from the example shows the result for conversions in both a checked an unchecked context. 您也可以使用編譯在 unchecked 內容中 Visual Basic 中執行的轉換/removeintchecks+編譯器參數和 C# 註解checked陳述式。You can perform conversions in an unchecked context in Visual Basic by compiling with the /removeintchecks+ compiler switch and in C# by commenting out the checked statement.

using System;

public class Example
{
   public static void Main()
   {
      Double[] values = { Double.MinValue, -67890.1234, -12345.6789,
                          12345.6789, 67890.1234, Double.MaxValue,
                          Double.NaN, Double.PositiveInfinity,
                          Double.NegativeInfinity };
      checked {
         foreach (var value in values) {
            try {
                Int64 lValue = (long) value;
                Console.WriteLine("{0} ({1}) --> {2} (0x{2:X16}) ({3})",
                                  value, value.GetType().Name,
                                  lValue, lValue.GetType().Name);
            }
            catch (OverflowException) {
               Console.WriteLine("Unable to convert {0} to Int64.", value);
            }
            try {
                UInt64 ulValue = (ulong) value;
                Console.WriteLine("{0} ({1}) --> {2} (0x{2:X16}) ({3})",
                                  value, value.GetType().Name,
                                  ulValue, ulValue.GetType().Name);
            }
            catch (OverflowException) {
               Console.WriteLine("Unable to convert {0} to UInt64.", value);
            }
            try {
                Decimal dValue = (decimal) value;
                Console.WriteLine("{0} ({1}) --> {2} ({3})",
                                  value, value.GetType().Name,
                                  dValue, dValue.GetType().Name);
            }
            catch (OverflowException) {
               Console.WriteLine("Unable to convert {0} to Decimal.", value);
            }
            try {
                Single sValue = (float) value;
                Console.WriteLine("{0} ({1}) --> {2} ({3})",
                                  value, value.GetType().Name,
                                  sValue, sValue.GetType().Name);
            }
            catch (OverflowException) {
               Console.WriteLine("Unable to convert {0} to Single.", value);
            }
            Console.WriteLine();
         }
      }
   }
}
// The example displays the following output for conversions performed
// in a checked context:
//       Unable to convert -1.79769313486232E+308 to Int64.
//       Unable to convert -1.79769313486232E+308 to UInt64.
//       Unable to convert -1.79769313486232E+308 to Decimal.
//       -1.79769313486232E+308 (Double) --> -Infinity (Single)
//
//       -67890.1234 (Double) --> -67890 (0xFFFFFFFFFFFEF6CE) (Int64)
//       Unable to convert -67890.1234 to UInt64.
//       -67890.1234 (Double) --> -67890.1234 (Decimal)
//       -67890.1234 (Double) --> -67890.13 (Single)
//
//       -12345.6789 (Double) --> -12345 (0xFFFFFFFFFFFFCFC7) (Int64)
//       Unable to convert -12345.6789 to UInt64.
//       -12345.6789 (Double) --> -12345.6789 (Decimal)
//       -12345.6789 (Double) --> -12345.68 (Single)
//
//       12345.6789 (Double) --> 12345 (0x0000000000003039) (Int64)
//       12345.6789 (Double) --> 12345 (0x0000000000003039) (UInt64)
//       12345.6789 (Double) --> 12345.6789 (Decimal)
//       12345.6789 (Double) --> 12345.68 (Single)
//
//       67890.1234 (Double) --> 67890 (0x0000000000010932) (Int64)
//       67890.1234 (Double) --> 67890 (0x0000000000010932) (UInt64)
//       67890.1234 (Double) --> 67890.1234 (Decimal)
//       67890.1234 (Double) --> 67890.13 (Single)
//
//       Unable to convert 1.79769313486232E+308 to Int64.
//       Unable to convert 1.79769313486232E+308 to UInt64.
//       Unable to convert 1.79769313486232E+308 to Decimal.
//       1.79769313486232E+308 (Double) --> Infinity (Single)
//
//       Unable to convert NaN to Int64.
//       Unable to convert NaN to UInt64.
//       Unable to convert NaN to Decimal.
//       NaN (Double) --> NaN (Single)
//
//       Unable to convert Infinity to Int64.
//       Unable to convert Infinity to UInt64.
//       Unable to convert Infinity to Decimal.
//       Infinity (Double) --> Infinity (Single)
//
//       Unable to convert -Infinity to Int64.
//       Unable to convert -Infinity to UInt64.
//       Unable to convert -Infinity to Decimal.
//       -Infinity (Double) --> -Infinity (Single)
// The example displays the following output for conversions performed
// in an unchecked context:
//       -1.79769313486232E+308 (Double) --> -9223372036854775808 (0x8000000000000000) (Int64)
//       -1.79769313486232E+308 (Double) --> 9223372036854775808 (0x8000000000000000) (UInt64)
//       Unable to convert -1.79769313486232E+308 to Decimal.
//       -1.79769313486232E+308 (Double) --> -Infinity (Single)
//
//       -67890.1234 (Double) --> -67890 (0xFFFFFFFFFFFEF6CE) (Int64)
//       -67890.1234 (Double) --> 18446744073709483726 (0xFFFFFFFFFFFEF6CE) (UInt64)
//       -67890.1234 (Double) --> -67890.1234 (Decimal)
//       -67890.1234 (Double) --> -67890.13 (Single)
//
//       -12345.6789 (Double) --> -12345 (0xFFFFFFFFFFFFCFC7) (Int64)
//       -12345.6789 (Double) --> 18446744073709539271 (0xFFFFFFFFFFFFCFC7) (UInt64)
//       -12345.6789 (Double) --> -12345.6789 (Decimal)
//       -12345.6789 (Double) --> -12345.68 (Single)
//
//       12345.6789 (Double) --> 12345 (0x0000000000003039) (Int64)
//       12345.6789 (Double) --> 12345 (0x0000000000003039) (UInt64)
//       12345.6789 (Double) --> 12345.6789 (Decimal)
//       12345.6789 (Double) --> 12345.68 (Single)
//
//       67890.1234 (Double) --> 67890 (0x0000000000010932) (Int64)
//       67890.1234 (Double) --> 67890 (0x0000000000010932) (UInt64)
//       67890.1234 (Double) --> 67890.1234 (Decimal)
//       67890.1234 (Double) --> 67890.13 (Single)
//
//       1.79769313486232E+308 (Double) --> -9223372036854775808 (0x8000000000000000) (Int64)
//       1.79769313486232E+308 (Double) --> 0 (0x0000000000000000) (UInt64)
//       Unable to convert 1.79769313486232E+308 to Decimal.
//       1.79769313486232E+308 (Double) --> Infinity (Single)
//
//       NaN (Double) --> -9223372036854775808 (0x8000000000000000) (Int64)
//       NaN (Double) --> 0 (0x0000000000000000) (UInt64)
//       Unable to convert NaN to Decimal.
//       NaN (Double) --> NaN (Single)
//
//       Infinity (Double) --> -9223372036854775808 (0x8000000000000000) (Int64)
//       Infinity (Double) --> 0 (0x0000000000000000) (UInt64)
//       Unable to convert Infinity to Decimal.
//       Infinity (Double) --> Infinity (Single)
//
//       -Infinity (Double) --> -9223372036854775808 (0x8000000000000000) (Int64)
//       -Infinity (Double) --> 9223372036854775808 (0x8000000000000000) (UInt64)
//       Unable to convert -Infinity to Decimal.
//       -Infinity (Double) --> -Infinity (Single)
Module Example
   Public Sub Main()
      Dim values() As Double = { Double.MinValue, -67890.1234, -12345.6789,
                                 12345.6789, 67890.1234, Double.MaxValue,
                                 Double.NaN, Double.PositiveInfinity,
                                 Double.NegativeInfinity }
      For Each value In values
         Try
             Dim lValue As Int64 = CLng(value)
             Console.WriteLine("{0} ({1}) --> {2} (0x{2:X16}) ({3})",
                               value, value.GetType().Name,
                               lValue, lValue.GetType().Name)
         Catch e As OverflowException
            Console.WriteLine("Unable to convert {0} to Int64.", value)
         End Try
         Try
             Dim ulValue As UInt64 = CULng(value)
             Console.WriteLine("{0} ({1}) --> {2} (0x{2:X16}) ({3})",
                               value, value.GetType().Name,
                               ulValue, ulValue.GetType().Name)
         Catch e As OverflowException
            Console.WriteLine("Unable to convert {0} to UInt64.", value)
         End Try
         Try
             Dim dValue As Decimal = CDec(value)
             Console.WriteLine("{0} ({1}) --> {2} ({3})",
                               value, value.GetType().Name,
                               dValue, dValue.GetType().Name)
         Catch e As OverflowException
            Console.WriteLine("Unable to convert {0} to Decimal.", value)
         End Try
         Try
             Dim sValue As Single = CSng(value)
             Console.WriteLine("{0} ({1}) --> {2} ({3})",
                               value, value.GetType().Name,
                               sValue, sValue.GetType().Name)
         Catch e As OverflowException
            Console.WriteLine("Unable to convert {0} to Single.", value)
         End Try
         Console.WriteLine()
      Next
   End Sub
End Module
' The example displays the following output for conversions performed
' in a checked context:
'       Unable to convert -1.79769313486232E+308 to Int64.
'       Unable to convert -1.79769313486232E+308 to UInt64.
'       Unable to convert -1.79769313486232E+308 to Decimal.
'       -1.79769313486232E+308 (Double) --> -Infinity (Single)
'
'       -67890.1234 (Double) --> -67890 (0xFFFFFFFFFFFEF6CE) (Int64)
'       Unable to convert -67890.1234 to UInt64.
'       -67890.1234 (Double) --> -67890.1234 (Decimal)
'       -67890.1234 (Double) --> -67890.13 (Single)
'
'       -12345.6789 (Double) --> -12346 (0xFFFFFFFFFFFFCFC6) (Int64)
'       Unable to convert -12345.6789 to UInt64.
'       -12345.6789 (Double) --> -12345.6789 (Decimal)
'       -12345.6789 (Double) --> -12345.68 (Single)
'
'       12345.6789 (Double) --> 12346 (0x000000000000303A) (Int64)
'       12345.6789 (Double) --> 12346 (0x000000000000303A) (UInt64)
'       12345.6789 (Double) --> 12345.6789 (Decimal)
'       12345.6789 (Double) --> 12345.68 (Single)
'
'       67890.1234 (Double) --> 67890 (0x0000000000010932) (Int64)
'       67890.1234 (Double) --> 67890 (0x0000000000010932) (UInt64)
'       67890.1234 (Double) --> 67890.1234 (Decimal)
'       67890.1234 (Double) --> 67890.13 (Single)
'
'       Unable to convert 1.79769313486232E+308 to Int64.
'       Unable to convert 1.79769313486232E+308 to UInt64.
'       Unable to convert 1.79769313486232E+308 to Decimal.
'       1.79769313486232E+308 (Double) --> Infinity (Single)
'
'       Unable to convert NaN to Int64.
'       Unable to convert NaN to UInt64.
'       Unable to convert NaN to Decimal.
'       NaN (Double) --> NaN (Single)
'
'       Unable to convert Infinity to Int64.
'       Unable to convert Infinity to UInt64.
'       Unable to convert Infinity to Decimal.
'       Infinity (Double) --> Infinity (Single)
'
'       Unable to convert -Infinity to Int64.
'       Unable to convert -Infinity to UInt64.
'       Unable to convert -Infinity to Decimal.
'       -Infinity (Double) --> -Infinity (Single)
' The example displays the following output for conversions performed
' in an unchecked context:
'       -1.79769313486232E+308 (Double) --> -9223372036854775808 (0x8000000000000000) (Int64)
'       -1.79769313486232E+308 (Double) --> 9223372036854775808 (0x8000000000000000) (UInt64)
'       Unable to convert -1.79769313486232E+308 to Decimal.
'       -1.79769313486232E+308 (Double) --> -Infinity (Single)
'
'       -67890.1234 (Double) --> -67890 (0xFFFFFFFFFFFEF6CE) (Int64)
'       -67890.1234 (Double) --> 18446744073709483726 (0xFFFFFFFFFFFEF6CE) (UInt64)
'       -67890.1234 (Double) --> -67890.1234 (Decimal)
'       -67890.1234 (Double) --> -67890.13 (Single)
'
'       -12345.6789 (Double) --> -12346 (0xFFFFFFFFFFFFCFC6) (Int64)
'       -12345.6789 (Double) --> 18446744073709539270 (0xFFFFFFFFFFFFCFC6) (UInt64)
'       -12345.6789 (Double) --> -12345.6789 (Decimal)
'       -12345.6789 (Double) --> -12345.68 (Single)
'
'       12345.6789 (Double) --> 12346 (0x000000000000303A) (Int64)
'       12345.6789 (Double) --> 12346 (0x000000000000303A) (UInt64)
'       12345.6789 (Double) --> 12345.6789 (Decimal)
'       12345.6789 (Double) --> 12345.68 (Single)
'
'       67890.1234 (Double) --> 67890 (0x0000000000010932) (Int64)
'       67890.1234 (Double) --> 67890 (0x0000000000010932) (UInt64)
'       67890.1234 (Double) --> 67890.1234 (Decimal)
'       67890.1234 (Double) --> 67890.13 (Single)
'
'       1.79769313486232E+308 (Double) --> -9223372036854775808 (0x8000000000000000) (Int64)
'       1.79769313486232E+308 (Double) --> 0 (0x0000000000000000) (UInt64)
'       Unable to convert 1.79769313486232E+308 to Decimal.
'       1.79769313486232E+308 (Double) --> Infinity (Single)
'
'       NaN (Double) --> -9223372036854775808 (0x8000000000000000) (Int64)
'       NaN (Double) --> 0 (0x0000000000000000) (UInt64)
'       Unable to convert NaN to Decimal.
'       NaN (Double) --> NaN (Single)
'
'       Infinity (Double) --> -9223372036854775808 (0x8000000000000000) (Int64)
'       Infinity (Double) --> 0 (0x0000000000000000) (UInt64)
'       Unable to convert Infinity to Decimal.
'       Infinity (Double) --> Infinity (Single)
'
'       -Infinity (Double) --> -9223372036854775808 (0x8000000000000000) (Int64)
'       -Infinity (Double) --> 9223372036854775808 (0x8000000000000000) (UInt64)
'       Unable to convert -Infinity to Decimal.
'       -Infinity (Double) --> -Infinity (Single)

如需有關轉換的數字類型的詳細資訊,請參閱.NET Framework 中的類型轉換類型轉換表For more information on the conversion of numeric types, see Type Conversion in the .NET Framework and Type Conversion Tables.

浮點數的功能Floating-Point Functionality

Double結構和相關的型別提供方法來執行作業,在下列區域:The Double structure and related types provide methods to perform operations in the following areas:

  • 值的比較Comparison of values. 您可以呼叫Equals方法,以判斷兩個Double值相等,或CompareTo方法,以判斷兩個值之間的關聯性。You can call the Equals method to determine whether two Double values are equal, or the CompareTo method to determine the relationship between two values.

    Double結構也支援一組完整的比較運算子。The Double structure also supports a complete set of comparison operators. 例如,您可以測試相等或不等,或判斷某個值是否大於或等於另一個。For example, you can test for equality or inequality, or determine whether one value is greater than or equal to another. 如果其中一個運算元不是數值的型別Double,則會轉換成Double之前執行比較。If one of the operands is a numeric type other than a Double, it is converted to a Double before performing the comparison.

    警告

    有效位數,因此兩個Double您預期是相等的值可能會變得不相等,這會影響比較的結果。Because of differences in precision, two Double values that you expect to be equal may turn out to be unequal, which affects the result of the comparison. 請參閱測試是否相等如需有關比較兩個區段Double值。See the Testing for Equality section for more information about comparing two Double values.

    您也可以呼叫IsNaNIsInfinityIsPositiveInfinity,和IsNegativeInfinity來測試這些特殊值的方法。You can also call the IsNaN, IsInfinity, IsPositiveInfinity, and IsNegativeInfinity methods to test for these special values.

  • 數學運算Mathematical operations. 常用的算術運算,例如加法、 減法、 乘法和除法、 會實作由語言編譯器和通用中間語言 (CIL) 的指示,而非Double方法。Common arithmetic operations, such as addition, subtraction, multiplication, and division, are implemented by language compilers and Common Intermediate Language (CIL) instructions, rather than by Double methods. 如果其中一個數學運算的運算元不是數值的型別Double,則會轉換成Double之前執行此作業。If one of the operands in a mathematical operation is a numeric type other than a Double, it is converted to a Double before performing the operation. 作業的結果也是Double值。The result of the operation is also a Double value.

    可以藉由呼叫執行其他數學運算static(Shared Visual Basic 中) 中的方法System.Math類別。Other mathematical operations can be performed by calling static (Shared in Visual Basic) methods in the System.Math class. 它包含常用的算術運算的其他方法 (例如Math.AbsMath.Sign,和Math.Sqrt),幾何 (例如Math.CosMath.Sin),和微積分 (例如Math.Log)。It includes additional methods commonly used for arithmetic (such as Math.Abs, Math.Sign, and Math.Sqrt), geometry (such as Math.Cos and Math.Sin), and calculus (such as Math.Log).

    您也可以使用操作中的個別位元Double值。You can also manipulate the individual bits in a Double value. BitConverter.DoubleToInt64Bits方法會保留Double值的位元模式中的 64 位元整數。The BitConverter.DoubleToInt64Bits method preserves a Double value's bit pattern in a 64-bit integer. BitConverter.GetBytes(Double)方法會傳回其位元模式中的位元組陣列。The BitConverter.GetBytes(Double) method returns its bit pattern in a byte array.

  • 捨入Rounding. 捨入通常用於一種技術以減少的差異值的浮點數表示和精確度的問題所造成的影響。Rounding is often used as a technique for reducing the impact of differences between values caused by problems of floating-point representation and precision. 您可以藉由四捨五入Double值,藉由呼叫Math.Round方法。You can round a Double value by calling the Math.Round method.

  • 格式化Formatting. 您可以將轉換Double值為其字串表示,藉由呼叫ToString方法或使用複合格式功能。You can convert a Double value to its string representation by calling the ToString method or by using the composite formatting feature. 如需格式字串的浮點值的字串表示的控制方式,請參閱標準數值格式字串自訂數值格式字串主題。For information about how format strings control the string representation of floating-point values, see the Standard Numeric Format Strings and Custom Numeric Format Strings topics.

  • 剖析字串Parsing strings. 您可以將轉換的浮點值的字串表示Double值,藉由呼叫ParseTryParse方法。You can convert the string representation of a floating-point value to a Double value by calling either the Parse or TryParse method. 如果剖析作業失敗,Parse方法會擲回例外狀況,而TryParse方法會傳回falseIf the parse operation fails, the Parse method throws an exception, whereas the TryParse method returns false.

  • 類型轉換Type conversion. Double結構提供的明確介面實作IConvertible介面支援任何兩個標準的.NET Framework 資料類型之間轉換。The Double structure provides an explicit interface implementation for the IConvertible interface, which supports conversion between any two standard .NET Framework data types. 語言編譯器也支援的所有其他標準數字型別,值隱含轉換Double值。Language compilers also support the implicit conversion of values of all other standard numeric types to Double values. 任何標準的數字型別,若要將值轉換Double是擴展轉換,而且不需要轉型運算子或轉換方法,使用者Conversion of a value of any standard numeric type to a Double is a widening conversion and does not require the user of a casting operator or conversion method,

    不過,轉換Int64Single值可能是遺失有效位數。However, conversion of Int64 and Single values can involve a loss of precision. 下表列出的每一種類型的有效位數的差異:The following table lists the differences in precision for each of these types:

    類型Type 最大有效位數Maximum precision 內部的有效位數Internal precision
    Double 1515 1717
    Int64 19 的十進位數字19 decimal digits 19 的十進位數字19 decimal digits
    Single 7 的十進位數字7 decimal digits 9 的十進位數字9 decimal digits

    有效位數的問題通常會影響Single值轉換成Double值。The problem of precision most frequently affects Single values that are converted to Double values. 在下列範例中,相同的除法運算所產生的兩個值相等因為其中一個值是單精確度浮點數值轉換成DoubleIn the following example, two values produced by identical division operations are unequal because one of the values is a single-precision floating point value converted to a Double.

    using System;
    
    public class Example
    {
       public static void Main()
       {
          Double value = .1;
          Double result1 = value * 10;
          Double result2 = 0;
          for (int ctr = 1; ctr <= 10; ctr++)
             result2 += value;
    
          Console.WriteLine(".1 * 10:           {0:R}", result1);
          Console.WriteLine(".1 Added 10 times: {0:R}", result2);
       }
    }
    // The example displays the following output:
    //       .1 * 10:           1
    //       .1 Added 10 times: 0.99999999999999989
    
    Module Example
       Public Sub Main()
          Dim value As Double = .1
          Dim result1 As Double = value * 10
          Dim result2 As Double
          For ctr As Integer = 1 To 10
             result2 += value
          Next
          Console.WriteLine(".1 * 10:           {0:R}", result1)
          Console.WriteLine(".1 Added 10 times: {0:R}", result2)
       End Sub
    End Module
    ' The example displays the following output:
    '       .1 * 10:           1
    '       .1 Added 10 times: 0.99999999999999989
    

欄位

Epsilon Epsilon Epsilon Epsilon

代表大於零的最小正 Double 值。Represents the smallest positive Double value that is greater than zero. 這個欄位是常數。This field is constant.

MaxValue MaxValue MaxValue MaxValue

表示 Double 最大的可能值。Represents the largest possible value of a Double. 這個欄位是常數。This field is constant.

MinValue MinValue MinValue MinValue

表示 Double 最小的可能值。Represents the smallest possible value of a Double. 這個欄位是常數。This field is constant.

NaN NaN NaN NaN

代表不是數字 (NaN) 的值。Represents a value that is not a number (NaN). 這個欄位是常數。This field is constant.

NegativeInfinity NegativeInfinity NegativeInfinity NegativeInfinity

表示負無限大。Represents negative infinity. 這個欄位是常數。This field is constant.

PositiveInfinity PositiveInfinity PositiveInfinity PositiveInfinity

表示正無限大。Represents positive infinity. 這個欄位是常數。This field is constant.

方法

CompareTo(Double) CompareTo(Double) CompareTo(Double) CompareTo(Double)

比較這個執行個體與雙精確度的浮點數值,並且傳回一個整數,指出這個執行個體的值是小於、等於或大於特定的雙精確度浮點數值。Compares this instance to a specified double-precision floating-point number and returns an integer that indicates whether the value of this instance is less than, equal to, or greater than the value of the specified double-precision floating-point number.

CompareTo(Object) CompareTo(Object) CompareTo(Object) CompareTo(Object)

比較這個執行個體與特定物件,並且傳回一個整數,指出這個執行個體的值是小於、等於或大於特定物件的值。Compares this instance to a specified object and returns an integer that indicates whether the value of this instance is less than, equal to, or greater than the value of the specified object.

Equals(Double) Equals(Double) Equals(Double) Equals(Double)

傳回數值,指示這個執行個體和指定的 Double 物件是否表示相同的值。Returns a value indicating whether this instance and a specified Double object represent the same value.

Equals(Object) Equals(Object) Equals(Object) Equals(Object)

傳回值,指出這個執行個體 (Instance) 是否和指定的物件相等。Returns a value indicating whether this instance is equal to a specified object.

GetHashCode() GetHashCode() GetHashCode() GetHashCode()

傳回這個執行個體的雜湊碼。Returns the hash code for this instance.

GetTypeCode() GetTypeCode() GetTypeCode() GetTypeCode()

傳回實值類型 TypeCodeDoubleReturns the TypeCode for value type Double.

IsFinite(Double) IsFinite(Double) IsFinite(Double) IsFinite(Double)
IsInfinity(Double) IsInfinity(Double) IsInfinity(Double) IsInfinity(Double)

傳回值,指出指定的數字是否計算結果為負或正的無限大。Returns a value indicating whether the specified number evaluates to negative or positive infinity

IsNaN(Double) IsNaN(Double) IsNaN(Double) IsNaN(Double)

傳回值,這個值表示指定的值是否不是數字 (NaN)。Returns a value that indicates whether the specified value is not a number (NaN).

IsNegative(Double) IsNegative(Double) IsNegative(Double) IsNegative(Double)
IsNegativeInfinity(Double) IsNegativeInfinity(Double) IsNegativeInfinity(Double) IsNegativeInfinity(Double)

傳回值,指出指定的數字是否計算結果為負的無限大。Returns a value indicating whether the specified number evaluates to negative infinity.

IsNormal(Double) IsNormal(Double) IsNormal(Double) IsNormal(Double)
IsPositiveInfinity(Double) IsPositiveInfinity(Double) IsPositiveInfinity(Double) IsPositiveInfinity(Double)

傳回值,指出指定數字是否計算結果為正的無限大。Returns a value indicating whether the specified number evaluates to positive infinity.

IsSubnormal(Double) IsSubnormal(Double) IsSubnormal(Double) IsSubnormal(Double)
Parse(String, NumberStyles, IFormatProvider) Parse(String, NumberStyles, IFormatProvider) Parse(String, NumberStyles, IFormatProvider) Parse(String, NumberStyles, IFormatProvider)

使用指定樣式和特定文化特性格式,將數字的字串表示轉換為其相等的雙精確度浮點數。Converts the string representation of a number in a specified style and culture-specific format to its double-precision floating-point number equivalent.

Parse(String, IFormatProvider) Parse(String, IFormatProvider) Parse(String, IFormatProvider) Parse(String, IFormatProvider)

將數字的字串表示 (使用指定的特定文化特性格式) 轉換為其相等的雙精確度浮點數。Converts the string representation of a number in a specified culture-specific format to its double-precision floating-point number equivalent.

Parse(ReadOnlySpan<Char>, NumberStyles, IFormatProvider) Parse(ReadOnlySpan<Char>, NumberStyles, IFormatProvider) Parse(ReadOnlySpan<Char>, NumberStyles, IFormatProvider) Parse(ReadOnlySpan<Char>, NumberStyles, IFormatProvider)
Parse(String) Parse(String) Parse(String) Parse(String)

將數字的字串表示轉換為其相等的雙精確度浮點數。Converts the string representation of a number to its double-precision floating-point number equivalent.

Parse(String, NumberStyles) Parse(String, NumberStyles) Parse(String, NumberStyles) Parse(String, NumberStyles)

將數字的字串表示 (使用指定樣式) 轉換為其相等的雙精確度浮點數。Converts the string representation of a number in a specified style to its double-precision floating-point number equivalent.

ToString(String, IFormatProvider) ToString(String, IFormatProvider) ToString(String, IFormatProvider) ToString(String, IFormatProvider)

使用指定的格式和特定文化特性格式資訊,將這個執行個體的數值轉換成它的相等字串表示。Converts the numeric value of this instance to its equivalent string representation using the specified format and culture-specific format information.

ToString(String) ToString(String) ToString(String) ToString(String)

使用指定格式,將這個執行個體的數值轉換成它的相等字串表示。Converts the numeric value of this instance to its equivalent string representation, using the specified format.

ToString(IFormatProvider) ToString(IFormatProvider) ToString(IFormatProvider) ToString(IFormatProvider)

使用指定的特定文化特性格式資訊,將這個執行個體的數值轉換成它的相等字串表示。Converts the numeric value of this instance to its equivalent string representation using the specified culture-specific format information.

ToString() ToString() ToString() ToString()

將這個執行個體的數值轉換為它的相等字串表示。Converts the numeric value of this instance to its equivalent string representation.

TryFormat(Span<Char>, Int32, ReadOnlySpan<Char>, IFormatProvider) TryFormat(Span<Char>, Int32, ReadOnlySpan<Char>, IFormatProvider) TryFormat(Span<Char>, Int32, ReadOnlySpan<Char>, IFormatProvider) TryFormat(Span<Char>, Int32, ReadOnlySpan<Char>, IFormatProvider)
TryParse(ReadOnlySpan<Char>, NumberStyles, IFormatProvider, Double) TryParse(ReadOnlySpan<Char>, NumberStyles, IFormatProvider, Double) TryParse(ReadOnlySpan<Char>, NumberStyles, IFormatProvider, Double) TryParse(ReadOnlySpan<Char>, NumberStyles, IFormatProvider, Double)
TryParse(String, Double) TryParse(String, Double) TryParse(String, Double) TryParse(String, Double)

將數字的字串表示轉換為其相等的雙精確度浮點數。Converts the string representation of a number to its double-precision floating-point number equivalent. 傳回值會指出轉換成功或失敗。A return value indicates whether the conversion succeeded or failed.

TryParse(ReadOnlySpan<Char>, Double) TryParse(ReadOnlySpan<Char>, Double) TryParse(ReadOnlySpan<Char>, Double) TryParse(ReadOnlySpan<Char>, Double)
TryParse(String, NumberStyles, IFormatProvider, Double) TryParse(String, NumberStyles, IFormatProvider, Double) TryParse(String, NumberStyles, IFormatProvider, Double) TryParse(String, NumberStyles, IFormatProvider, Double)

使用指定樣式和特定文化特性格式,將數字的字串表示轉換為其相等的雙精確度浮點數。Converts the string representation of a number in a specified style and culture-specific format to its double-precision floating-point number equivalent. 傳回值會指出轉換成功或失敗。A return value indicates whether the conversion succeeded or failed.

運算子

Equality(Double, Double) Equality(Double, Double) Equality(Double, Double) Equality(Double, Double)

傳回值,這個值表示兩個指定的 Double 值是否相等。Returns a value that indicates whether two specified Double values are equal.

GreaterThan(Double, Double) GreaterThan(Double, Double) GreaterThan(Double, Double) GreaterThan(Double, Double)

傳回值,這個值表示指定的 Double 值是否大於另一個指定的 Double 值。Returns a value that indicates whether a specified Double value is greater than another specified Double value.

GreaterThanOrEqual(Double, Double) GreaterThanOrEqual(Double, Double) GreaterThanOrEqual(Double, Double) GreaterThanOrEqual(Double, Double)

傳回值,這個值表示指定的 Double 值是否大於或等於另一個指定的 Double 值。Returns a value that indicates whether a specified Double value is greater than or equal to another specified Double value.

Inequality(Double, Double) Inequality(Double, Double) Inequality(Double, Double) Inequality(Double, Double)

傳回值,這個值表示兩個指定的 Double 值是否不相等。Returns a value that indicates whether two specified Double values are not equal.

LessThan(Double, Double) LessThan(Double, Double) LessThan(Double, Double) LessThan(Double, Double)

傳回值,這個值表示指定的 Double 值是否小於另一個指定的 Double 值。Returns a value that indicates whether a specified Double value is less than another specified Double value.

LessThanOrEqual(Double, Double) LessThanOrEqual(Double, Double) LessThanOrEqual(Double, Double) LessThanOrEqual(Double, Double)

傳回值,這個值表示指定的 Double 值是否小於或等於另一個指定的 Double 值。Returns a value that indicates whether a specified Double value is less than or equal to another specified Double value.

明確介面實作

IComparable.CompareTo(Object) IComparable.CompareTo(Object) IComparable.CompareTo(Object) IComparable.CompareTo(Object)
IConvertible.GetTypeCode() IConvertible.GetTypeCode() IConvertible.GetTypeCode() IConvertible.GetTypeCode()
IConvertible.ToBoolean(IFormatProvider) IConvertible.ToBoolean(IFormatProvider) IConvertible.ToBoolean(IFormatProvider) IConvertible.ToBoolean(IFormatProvider)

如需這個成員的說明,請參閱 ToBoolean(IFormatProvider)For a description of this member, see ToBoolean(IFormatProvider).

IConvertible.ToByte(IFormatProvider) IConvertible.ToByte(IFormatProvider) IConvertible.ToByte(IFormatProvider) IConvertible.ToByte(IFormatProvider)

如需這個成員的說明,請參閱 ToByte(IFormatProvider)For a description of this member, see ToByte(IFormatProvider).

IConvertible.ToChar(IFormatProvider) IConvertible.ToChar(IFormatProvider) IConvertible.ToChar(IFormatProvider) IConvertible.ToChar(IFormatProvider)

不支援這個轉換。This conversion is not supported. 嘗試使用這個方法會擲回 InvalidCastExceptionAttempting to use this method throws an InvalidCastException.

IConvertible.ToDateTime(IFormatProvider) IConvertible.ToDateTime(IFormatProvider) IConvertible.ToDateTime(IFormatProvider) IConvertible.ToDateTime(IFormatProvider)

不支援這個轉換。This conversion is not supported. 嘗試使用這個方法會擲回 InvalidCastExceptionAttempting to use this method throws an InvalidCastException

IConvertible.ToDecimal(IFormatProvider) IConvertible.ToDecimal(IFormatProvider) IConvertible.ToDecimal(IFormatProvider) IConvertible.ToDecimal(IFormatProvider)

如需這個成員的說明,請參閱 ToDecimal(IFormatProvider)For a description of this member, see ToDecimal(IFormatProvider).

IConvertible.ToDouble(IFormatProvider) IConvertible.ToDouble(IFormatProvider) IConvertible.ToDouble(IFormatProvider) IConvertible.ToDouble(IFormatProvider)

如需這個成員的說明,請參閱 ToDouble(IFormatProvider)For a description of this member, see ToDouble(IFormatProvider).

IConvertible.ToInt16(IFormatProvider) IConvertible.ToInt16(IFormatProvider) IConvertible.ToInt16(IFormatProvider) IConvertible.ToInt16(IFormatProvider)

如需這個成員的說明,請參閱 ToInt16(IFormatProvider)For a description of this member, see ToInt16(IFormatProvider).

IConvertible.ToInt32(IFormatProvider) IConvertible.ToInt32(IFormatProvider) IConvertible.ToInt32(IFormatProvider) IConvertible.ToInt32(IFormatProvider)

如需這個成員的說明,請參閱 ToInt32(IFormatProvider)For a description of this member, see ToInt32(IFormatProvider).

IConvertible.ToInt64(IFormatProvider) IConvertible.ToInt64(IFormatProvider) IConvertible.ToInt64(IFormatProvider) IConvertible.ToInt64(IFormatProvider)

如需這個成員的說明,請參閱 ToInt64(IFormatProvider)For a description of this member, see ToInt64(IFormatProvider).

IConvertible.ToSByte(IFormatProvider) IConvertible.ToSByte(IFormatProvider) IConvertible.ToSByte(IFormatProvider) IConvertible.ToSByte(IFormatProvider)

如需這個成員的說明,請參閱 ToSByte(IFormatProvider)For a description of this member, see ToSByte(IFormatProvider).

IConvertible.ToSingle(IFormatProvider) IConvertible.ToSingle(IFormatProvider) IConvertible.ToSingle(IFormatProvider) IConvertible.ToSingle(IFormatProvider)

如需這個成員的說明,請參閱 ToSingle(IFormatProvider)For a description of this member, see ToSingle(IFormatProvider).

IConvertible.ToType(Type, IFormatProvider) IConvertible.ToType(Type, IFormatProvider) IConvertible.ToType(Type, IFormatProvider) IConvertible.ToType(Type, IFormatProvider)

如需這個成員的說明,請參閱 ToType(Type, IFormatProvider)For a description of this member, see ToType(Type, IFormatProvider).

IConvertible.ToUInt16(IFormatProvider) IConvertible.ToUInt16(IFormatProvider) IConvertible.ToUInt16(IFormatProvider) IConvertible.ToUInt16(IFormatProvider)

如需這個成員的說明,請參閱 ToUInt16(IFormatProvider)For a description of this member, see ToUInt16(IFormatProvider).

IConvertible.ToUInt32(IFormatProvider) IConvertible.ToUInt32(IFormatProvider) IConvertible.ToUInt32(IFormatProvider) IConvertible.ToUInt32(IFormatProvider)

如需這個成員的說明,請參閱 ToUInt32(IFormatProvider)For a description of this member, see ToUInt32(IFormatProvider).

IConvertible.ToUInt64(IFormatProvider) IConvertible.ToUInt64(IFormatProvider) IConvertible.ToUInt64(IFormatProvider) IConvertible.ToUInt64(IFormatProvider)

如需這個成員的說明,請參閱 ToUInt64(IFormatProvider)For a description of this member, see ToUInt64(IFormatProvider).

適用於

執行緒安全性

此型別的所有成員都是安全執行緒。All members of this type are thread safe. 若要修改執行個體狀態會顯示的成員實際上會傳回新的值進行初始化的新執行個體。Members that appear to modify instance state actually return a new instance initialized with the new value. 為與任何其他型別,讀取和寫入共用的變數,其中包含這個型別的執行個體必須受到鎖定,以確保執行緒安全性。As with any other type, reading and writing to a shared variable that contains an instance of this type must be protected by a lock to guarantee thread safety.

另請參閱