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IsSurrogatePair Method (String, Int32)
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Char.IsSurrogatePair Method (String, Int32)

Indicates whether two adjacent Char objects at a specified position in a string form a surrogate pair.

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

'Declaration
Public Shared Function IsSurrogatePair ( _
	s As String, _
	index As Integer _
) As Boolean

Parameters

s
Type: System.String

A string.

index
Type: System.Int32

The starting position of the pair of characters to evaluate within s.

Return Value

Type: System.Boolean
true if the s parameter includes adjacent characters at positions index and index + 1, and the numeric value of the character at position index ranges from U+D800 through U+DBFF, and the numeric value of the character at position index+1 ranges from U+DC00 through U+DFFF; otherwise, false.

ExceptionCondition
ArgumentNullException

s is Nothing.

ArgumentOutOfRangeException

index is not a position within s.

Ordinarily, a single character is represented by a single 16-bit Unicode code unit. UTF-16 encoding also supports surrogate pairs, which allow a single abstract character to be represented by two 16-bit code units. The first code unit, whose value can range from U+D800 to U+DBFF, is the high surrogate. The second code unit, whose value can range from U+DC00 to U+DFFF, is the low surrogate. Individual surrogate code points have no interpretation of their own. For more information about surrogates and the Unicode Standard, see the Unicode home page.

The following code example demonstrates the IsHighSurrogate, IsLowSurrogate, and IsSurrogatePair methods.

' This example demonstrates the Char.IsLowSurrogate() method 
'                                    IsHighSurrogate() method 
'                                    IsSurrogatePair() method 
Imports System
Imports Microsoft.VisualBasic

Class Sample
   Public Shared Sub Main()
      Dim cHigh As Char = ChrW(&HD800)
      Dim cLow  As Char = ChrW(&HDC00)
      Dim s1 = New [String](New Char() {"a"c, ChrW(&HD800), ChrW(&HDC00), "z"c})
      Dim divider As String = [String].Concat(Environment.NewLine, _
                                              New [String]("-"c, 70), _
                                              Environment.NewLine)

      Console.WriteLine()
      Console.WriteLine("Hexadecimal code point of the character, cHigh: {0:X4}", AscW(cHigh))
      Console.WriteLine("Hexadecimal code point of the character, cLow:  {0:X4}", AscW(cLow))
      Console.WriteLine()
      Console.WriteLine("Characters in string, s1: 'a', high surrogate, low surrogate, 'z'")
      Console.WriteLine("Hexadecimal code points of the characters in string, s1: ")
      Dim i As Integer 
      For i = 0 To s1.Length - 1
         Console.WriteLine("s1({0}) = {1:X4} ", i, AscW(s1.Chars(i)))
      Next i
      Console.WriteLine(divider)

      Console.WriteLine("Is each of the following characters a high surrogate?")
      Console.WriteLine("A1) cLow?  - {0}", [Char].IsHighSurrogate(cLow))
      Console.WriteLine("A2) cHigh? - {0}", [Char].IsHighSurrogate(cHigh))
      Console.WriteLine("A3) s1(0)? - {0}", [Char].IsHighSurrogate(s1, 0))
      Console.WriteLine("A4) s1(1)? - {0}", [Char].IsHighSurrogate(s1, 1))
      Console.WriteLine(divider)

      Console.WriteLine("Is each of the following characters a low surrogate?")
      Console.WriteLine("B1) cLow?  - {0}", [Char].IsLowSurrogate(cLow))
      Console.WriteLine("B2) cHigh? - {0}", [Char].IsLowSurrogate(cHigh))
      Console.WriteLine("B3) s1(0)? - {0}", [Char].IsLowSurrogate(s1, 0))
      Console.WriteLine("B4) s1(2)? - {0}", [Char].IsLowSurrogate(s1, 2))
      Console.WriteLine(divider)

      Console.WriteLine("Is each of the following pairs of characters a surrogate pair?")
      Console.WriteLine("C1) cHigh and cLow?  - {0}", [Char].IsSurrogatePair(cHigh, cLow))
      Console.WriteLine("C2) s1(0) and s1(1)? - {0}", [Char].IsSurrogatePair(s1, 0))
      Console.WriteLine("C3) s1(1) and s1(2)? - {0}", [Char].IsSurrogatePair(s1, 1))
      Console.WriteLine("C4) s1(2) and s1(3)? - {0}", [Char].IsSurrogatePair(s1, 2))
      Console.WriteLine(divider)
   End Sub 'Main
End Class 'Sample

'This example produces the following results: 

'Hexadecimal code point of the character, cHigh: D800 
'Hexadecimal code point of the character, cLow:  DC00 

'Characters in string, s1: 'a', high surrogate, low surrogate, 'z' 
'Hexadecimal code points of the characters in string, s1: 
's1(0) = 0061 
's1(1) = D800 
's1(2) = DC00 
's1(3) = 007A 

'---------------------------------------------------------------------- 

'Is each of the following characters a high surrogate? 
'A1) cLow?  - False 
'A2) cHigh? - True 
'A3) s1(0)? - False 
'A4) s1(1)? - True 

'---------------------------------------------------------------------- 

'Is each of the following characters a low surrogate? 
'B1) cLow?  - True 
'B2) cHigh? - False 
'B3) s1(0)? - False 
'B4) s1(2)? - True 

'---------------------------------------------------------------------- 

'Is each of the following pairs of characters a surrogate pair? 
'C1) cHigh and cLow?  - True 
'C2) s1(0) and s1(1)? - False 
'C3) s1(1) and s1(2)? - True 
'C4) s1(2) and s1(3)? - False 

'---------------------------------------------------------------------- 
'

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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