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UTF32Encoding.GetMaxByteCount Method

Calculates the maximum number of bytes produced by encoding the specified number of characters.

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

'Declaration
Public Overrides Function GetMaxByteCount ( _
	charCount As Integer _
) As Integer

Parameters

charCount
Type: System.Int32

The number of characters to encode.

Return Value

Type: System.Int32
The maximum number of bytes produced by encoding the specified number of characters.

ExceptionCondition
ArgumentOutOfRangeException

charCount is less than zero.

-or-

The resulting number of bytes is greater than the maximum number that can be returned as an integer.

EncoderFallbackException

A fallback occurred (see Character Encoding in the .NET Framework for complete explanation)

-and-

EncoderFallback is set to EncoderExceptionFallback.

To calculate the exact array size required by GetBytes to store the resulting bytes, the application uses GetByteCount. To calculate the maximum array size, the application should use GetMaxByteCount. The GetByteCount method generally allows allocation of less memory, while the GetMaxByteCount method generally executes faster.

GetMaxByteCount is a worst-case number, including the worst case for the currently selected EncoderFallback. If a fallback is chosen with a potentially large string, M GetMaxByteCount can return large values.

In most cases, this method returns reasonable numbers for small strings. For large strings, you might have to choose between using very large buffers and catching errors in the rare case that a more reasonable buffer is exceeded. You might also want to consider a different approach and use GetByteCount or Encoder.Convert.

GetMaxByteCount has no relation to GetChars. If your application needs a similar function to use with GetChars, it should use GetMaxCharCount.

NoteNote

GetMaxByteCount(N) is not necessarily the same value as N* GetMaxByteCount(1).

The following code example determines the number of bytes required to encode a string, then encodes the string and displays the resulting bytes.

Imports System
Imports System.Text
Imports Microsoft.VisualBasic

Public Class SamplesUTF32Encoding   

   Public Shared Sub Main()

      ' The characters to encode: 
      '    Latin Small Letter Z (U+007A) 
      '    Latin Small Letter A (U+0061) 
      '    Combining Breve (U+0306) 
      '    Latin Small Letter AE With Acute (U+01FD) 
      '    Greek Small Letter Beta (U+03B2) 
      '    a high-surrogate value (U+D8FF) 
      '    a low-surrogate value (U+DCFF) 
      Dim myStr As String = "za" & ChrW(&H0306) & ChrW(&H01FD) & ChrW(&H03B2) & ChrW(&HD8FF) & ChrW(&HDCFF)

      ' Create instances of different encodings. 
      Dim u7 As New UTF7Encoding()
      Dim u8Nobom As New UTF8Encoding(False, True)
      Dim u8Bom As New UTF8Encoding(True, True)
      Dim u32Nobom As New UTF32Encoding(False, False, True)
      Dim u32Bom As New UTF32Encoding(False, True, True)

      ' Get the byte counts and the bytes.
      PrintCountsAndBytes(myStr, u7)
      PrintCountsAndBytes(myStr, u8Nobom)
      PrintCountsAndBytes(myStr, u8Bom)
      PrintCountsAndBytes(myStr, u32Nobom)
      PrintCountsAndBytes(myStr, u32Bom)

   End Sub 'Main


   Public Shared Sub PrintCountsAndBytes(s As String, enc As Encoding)

      ' Display the name of the encoding used.
      Console.Write("{0,-25} :", enc.ToString())

      ' Display the exact byte count. 
      Dim iBC As Integer = enc.GetByteCount(s)
      Console.Write(" {0,-3}", iBC)

      ' Display the maximum byte count. 
      Dim iMBC As Integer = enc.GetMaxByteCount(s.Length)
      Console.Write(" {0,-3} :", iMBC)

      ' Get the byte order mark, if any. 
      Dim preamble As Byte() = enc.GetPreamble()

      ' Combine the preamble and the encoded bytes. 
      ' NOTE: In Visual Basic, arrays contain one extra element by default. 
      '       The following line creates an array with the exact number of elements required. 
      Dim bytes(preamble.Length + iBC - 1) As Byte
      Array.Copy(preamble, bytes, preamble.Length)
      enc.GetBytes(s, 0, s.Length, bytes, preamble.Length)

      ' Display all the encoded bytes.
      PrintHexBytes(bytes)

   End Sub 'PrintCountsAndBytes


   Public Shared Sub PrintHexBytes(bytes() As Byte)

      If bytes Is Nothing OrElse bytes.Length = 0 Then
         Console.WriteLine("<none>")
      Else 
         Dim i As Integer 
         For i = 0 To bytes.Length - 1
            Console.Write("{0:X2} ", bytes(i))
         Next i
         Console.WriteLine()
      End If 

   End Sub 'PrintHexBytes 

End Class 'SamplesUTF32Encoding


'This code produces the following output. 

'System.Text.UTF7Encoding  : 18  23  :7A 61 2B 41 77 59 42 2F 51 4F 79 32 50 2F 63 2F 77 2D 
'System.Text.UTF8Encoding  : 12  24  :7A 61 CC 86 C7 BD CE B2 F1 8F B3 BF 
'System.Text.UTF8Encoding  : 12  24  :EF BB BF 7A 61 CC 86 C7 BD CE B2 F1 8F B3 BF 
'System.Text.UTF32Encoding : 24  28  :7A 00 00 00 61 00 00 00 06 03 00 00 FD 01 00 00 B2 03 00 00 FF FC 04 00 
'System.Text.UTF32Encoding : 24  28  :FF FE 00 00 7A 00 00 00 61 00 00 00 06 03 00 00 FD 01 00 00 B2 03 00 00 FF FC 04 00

.NET Framework

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

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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