Článek
11/18/2011

Double Structure

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Represents a double-precision floating-point number.

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
<ComVisibleAttribute(True)> _
Public Structure Double _
    Implements IComparable, IFormattable, IConvertible, IComparable(Of Double),  _
    IEquatable(Of Double)

[ComVisibleAttribute(true)]
public struct Double : IComparable, IFormattable, 
    IConvertible, IComparable<double>, IEquatable<double>

The Double type exposes the following members.

Methods

	Name	Description
	CompareTo(Double)	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)	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)	Returns a value indicating whether this instance and a specified Double object represent the same value.
	Equals(Object)	Returns a value indicating whether this instance is equal to a specified object. (Overrides ValueType.Equals(Object).)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Returns the hash code for this instance. (Overrides ValueType.GetHashCode().)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	GetTypeCode	Returns the TypeCode for value type Double.
	IsInfinity	Returns a value indicating whether the specified number evaluates to negative or positive infinity
	IsNaN	Returns a value indicating whether the specified number evaluates to a value that is not a number (NaN).
	IsNegativeInfinity	Returns a value indicating whether the specified number evaluates to negative infinity.
	IsPositiveInfinity	Returns a value indicating whether the specified number evaluates to positive infinity.
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	Parse(String)	Converts the string representation of a number to its double-precision floating-point number equivalent.
	Parse(String, NumberStyles)	Converts the string representation of a number in a specified style to its double-precision floating-point number equivalent.
	Parse(String, IFormatProvider)	Converts the string representation of a number in a specified culture-specific format to its double-precision floating-point number equivalent.
	Parse(String, NumberStyles, IFormatProvider)	Converts the string representation of a number in a specified style and culture-specific format to its double-precision floating-point number equivalent.
	ToString()	Converts the numeric value of this instance to its equivalent string representation. (Overrides ValueType.ToString().)
	ToString(IFormatProvider)	Converts the numeric value of this instance to its equivalent string representation using the specified culture-specific format information.
	ToString(String)	Converts the numeric value of this instance to its equivalent string representation, using the specified format.
	ToString(String, IFormatProvider)	Converts the numeric value of this instance to its equivalent string representation using the specified format and culture-specific format information.
	TryParse(String, Double%)	Converts the string representation of a number to its double-precision floating-point number equivalent. A return value indicates whether the conversion succeeded or failed.
	TryParse(String, NumberStyles, IFormatProvider, Double%)	Converts the string representation of a number in a specified style and culture-specific format to its double-precision floating-point number equivalent. A return value indicates whether the conversion succeeded or failed.

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Fields

	Name	Description
	Epsilon	Represents the smallest positive Double value greater than zero. This field is constant.
	MaxValue	Represents the largest possible value of a Double. This field is constant.
	MinValue	Represents the smallest possible value of a Double. This field is constant.
	NaN	Represents a value that is not a number (NaN). This field is constant.
	NegativeInfinity	Represents negative infinity. This field is constant.
	PositiveInfinity	Represents positive infinity. This field is constant.

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Explicit Interface Implementations

	Name	Description
	IConvertible.ToBoolean	Infrastructure. For a description of this member, see IConvertible.ToBoolean.
	IConvertible.ToByte	Infrastructure. For a description of this member, see IConvertible.ToByte.
	IConvertible.ToChar	Infrastructure. This conversion is not supported. Attempting to use this method throws an InvalidCastException.
	IConvertible.ToDateTime	Infrastructure. This conversion is not supported. Attempting to use this method throws an InvalidCastException
	IConvertible.ToDecimal	Infrastructure. For a description of this member, see IConvertible.ToDecimal.
	IConvertible.ToDouble	Infrastructure. For a description of this member, see IConvertible.ToDouble.
	IConvertible.ToInt16	Infrastructure. For a description of this member, see IConvertible.ToInt16.
	IConvertible.ToInt32	Infrastructure. For a description of this member, see IConvertible.ToInt32.
	IConvertible.ToInt64	Infrastructure. For a description of this member, see IConvertible.ToInt64.
	IConvertible.ToSByte	Infrastructure. For a description of this member, see IConvertible.ToSByte.
	IConvertible.ToSingle	Infrastructure. For a description of this member, see IConvertible.ToSingle.
	IConvertible.ToType	Infrastructure. For a description of this member, see IConvertible.ToType.
	IConvertible.ToUInt16	Infrastructure. For a description of this member, see IConvertible.ToUInt16.
	IConvertible.ToUInt32	Infrastructure. For a description of this member, see IConvertible.ToUInt32.
	IConvertible.ToUInt64	Infrastructure. For a description of this member, see IConvertible.ToUInt64.

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Remarks

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).

Double complies with the IEC 60559:1989 (IEEE 754) standard for binary floating-point arithmetic.

Double provides methods to compare instances of this type, convert the value of an instance to its string representation, and convert the string representation of a number to an instance of this type. For information about how format specification codes control the string representation of value types, see Formatting Types, Standard Numeric Format Strings, and Custom Numeric Format Strings.

Using Floating-Point Numbers

When performing binary operations, if one of the operands is a Double, then the other operand is required to be an integral type or a floating-point type (Double or Single). Prior to performing the operation, if the other operand is not a Double, it is converted to Double, and the operation is performed using at least Double range and precision. If the operation produces a numeric result, the type of the result is Double.

The floating-point operators, including the assignment operators, do not throw exceptions. Instead, in exceptional situations the result of a floating-point operation is zero, infinity, or NaN, as described below:

If the result of a floating-point operation is too small for the destination format, the result of the operation is zero.
If the magnitude of the result of a floating-point operation is too large for the destination format, the result of the operation is PositiveInfinity or NegativeInfinity, as appropriate for the sign of the result.
If a floating-point operation is invalid, the result of the operation is NaN.
If one or both operands of a floating-point operation are NaN, the result of the operation is NaN.

Floating-Point Values and Loss of Precision

Remember that a floating-point number can only approximate a decimal number, and that the precision of a floating-point number determines how accurately that number approximates a decimal number. By default, a Double value contains 15 decimal digits of precision, although a maximum of 17 digits is maintained internally. The precision of a floating-point number has several consequences:

Two floating-point numbers that appear equal for a particular precision might not compare equal because their least significant digits are different.
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 floating-point number might not exactly approximate the decimal number.
A value might not roundtrip if a floating-point number is involved. A value is said to roundtrip 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 equal to the original floating-point number. The roundtrip might fail because one or more least significant digits are lost or changed in a conversion.

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.

Interface Implementations

This type implements the interfaces IComparable, IComparable<T>, IFormattable, and IConvertible. Use the Convert class for conversions instead of this type's explicit interface member implementation of IConvertible.

Double Values and Silverlight XAML Parsing

When a Double value is processed from Silverlight XAML as a XAML attribute value, the value does not preserve the full precision that is implied by the definition of Double in code and the runtime. This is due to native code being used as part of the Silverlight XAML parser operations, and deliberate optimization for numeric values that are applicable to a user interface. For more information, see XAML Usage Syntax.

Silverlight also includes several properties where the underlying property type is Double, but where the expected values fall between 0 and 1.0. This is typically noted in the reference documentation for that property, and often is noted in the XAML syntax specifically. An example of such a property is UIElement.Opacity.

Examples

The following example illustrates the use of Double:

' 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 obj Is Nothing Then Return 1

      Dim temp As Temperature = TryCast(obj, Temperature)
      If temp IsNot Nothing Then
         Return m_value.CompareTo(temp.m_value)
      Else
         Throw New ArgumentException("object is not a Temperature")
      End If
   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

// Temperature class stores the value as 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 (temp != 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 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;
      }
   }
}

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

All members of this type are thread safe. Members that appear to modify instance state actually return a new instance initialized with the new value. 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.

Caution:
Assigning an instance of this type is not thread safe on all hardware platforms because the binary representation of that instance might be too large to assign in a single atomic operation.

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