Articolo
11/18/2011

Char.IsNumber Method (Char)

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Updated: December 2010

Indicates whether the specified Unicode character is categorized as a number.

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

Syntax

'Declaration
Public Shared Function IsNumber ( _
    c As Char _
) As Boolean

public static bool IsNumber(
    char c
)

Parameters

c
Type: System.Char
A Unicode character.

Return Value

Type: System.Boolean
true if c is a number; otherwise, false.

Remarks

This method determines if a Char is of any numeric Unicode category. In addition to digits, numbers include characters, fractions, subscripts, superscripts, Roman numerals, currency numerators, and encircled numbers. This method contrasts with the IsDigit method, which determines if a Char is a radix-10 digit.

Valid numbers are members of the UnicodeCategory.DecimalDigitNumber, UnicodeCategory.LetterNumber, or UnicodeCategory.OtherNumber category.

The IsNumber method assumes that c corresponds to a single linguistic character and checks whether that character represents a number. 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 uses the ConvertFromUtf32 method to instantiate a string that represents AEGEAN NUMBER ONE. As the output from the example shows, the IsNumber 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), 
                                    Char.IsNumber(ch)) + vbCrLf
Next
' The example displays the following output:
'       U+D800: False
'       U+DD07: False

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

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

Examples

The following example demonstrates IsNumber.


Module Example

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

      Dim str As String
      str = "non-numeric"

      outputBlock.Text &= Char.IsNumber("8"c) & vbCrLf      ' Output: "True"
      outputBlock.Text += String.Format(Char.IsNumber(str, 3)) & vbCrLf    ' Output: "False"

   End Sub

End Module

using System;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      string str = "non-numeric";

      outputBlock.Text += Char.IsNumber('8').ToString() + "\n";     
      outputBlock.Text += Char.IsNumber(str, 3).ToString() + "\n";
   }
}
// This example produces the following output:
//       True  
//       False

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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