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11/18/2011

Char.GetNumericValue Method (Char)

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Updated: December 2010

Converts the specified numeric Unicode character to a double-precision floating point number.

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

Syntax

'Declaration
Public Shared Function GetNumericValue ( _
    c As Char _
) As Double

public static double GetNumericValue(
    char c
)

Parameters

c
Type: System.Char
A Unicode character.

Return Value

Type: System.Double
The numeric value of c if that character represents a number; otherwise, -1.0.

Remarks

The c parameter must be the Char representation of a numeric value. For example, if c is '5', the return value is 5. However, if c is 'z', the return value is -1.0.

A character has an associated numeric value if and only if it is a member of one of the following UnicodeCategory categories: DecimalDigitNumber, LetterNumber, or OtherNumber.

The GetNumericValue method assumes that c corresponds to a single linguistic character and checks whether that character can be converted to a decimal digit. However, some numbers in the Unicode standard are represented by two Char objects that form a surrogate pair. For example, the Aegean numbering system consists of code points U+10107 through U+10133. The following example instantiates a string that represents AEGEAN NUMBER ONE. As the output from the example shows, the GetNumericValue method returns false if it is passed either a high surrogate or a low surrogate of this character.

Dim surrogate As String = ChrW(&HD800) + ChrW(&HDD07)     ' AEGEAN NUMBER ONE
For Each ch In surrogate
   outputBlock.Text += String.Format("U+{0:X4}: {1}    ", Convert.ToUInt16(ch) & vbCrLf, 
                                          Char.GetNumericValue(ch))
Next
' The example displays the following output:
'       U+D800: -1
'       U+DD07: -1

string surrogate = "\uD800\uDD07";            // AEGEAN NUMBER ONE
foreach (var ch in surrogate)
   outputBlock.Text += String.Format("U+{0:X4}: {1}    ", Convert.ToUInt16(ch),
                                          Char.GetNumericValue(ch)) + "\n";

// The example displays the following output:
//       U+D800: -1
//       U+DD07: -1

Examples

The following example demonstrates GetNumericValue.


Module Example

   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      Dim str As String
      str = "input: 1"

      outputBlock.Text &= Char.GetNumericValue("8"c) & vbCrLf       ' Output: "8"
      outputBlock.Text += String.Format(Char.GetNumericValue(str, 7)) & vbCrLf     ' Output: "1"

   End Sub

End Module

using System;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string str = "input: 1";

      outputBlock.Text += Char.GetNumericValue('8') + "\n";        // Output: "8"
      outputBlock.Text += Char.GetNumericValue(str, 7) + "\n";     // Output: "1"
   }
}

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.

Change History

Date	History	Reason
December 2010	Added information about how the method handles surrogate pairs.	Information enhancement.

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