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Encoding.GetCharCount Method (Byte())

When overridden in a derived class, calculates the number of characters produced by decoding all the bytes in the specified byte array.

Namespace:  System.Text
Assemblies:   System.Text.Encoding (in System.Text.Encoding.dll)
  mscorlib (in mscorlib.dll)

'Declaration
Public Overridable Function GetCharCount ( _
	bytes As Byte() _
) As Integer

Parameters

bytes
Type: System.Byte()

The byte array containing the sequence of bytes to decode.

Return Value

Type: System.Int32
The number of characters produced by decoding the specified sequence of bytes.

ExceptionCondition
ArgumentNullException

bytes is Nothing.

DecoderFallbackException

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

-and-

DecoderFallback is set to DecoderExceptionFallback.

To calculate the exact array size required by GetChars(Byte()) to store the resulting characters, you should use the GetCharCount(Byte()) method. To calculate the maximum array size, you should use the GetMaxCharCount(Int32) method. The GetCharCount(Byte()) method generally allows allocation of less memory, while the GetMaxCharCount method generally executes faster.

The GetCharCount(Byte()) method determines how many characters result in decoding a sequence of bytes, and the GetChars(Byte()) method performs the actual decoding. The Encoding.GetChars method expects discrete conversions, in contrast to the Decoder.GetChars method, which handles multiple passes on a single input stream.

Several versions of GetCharCount and GetChars are supported. The following are some programming considerations for use of these methods:

  • Your app might need to decode multiple input bytes from a code page and process the bytes using multiple calls. In this case, you probably need to maintain state between calls.

  • If your app handles string outputs, you should use the GetString method. Since this method must check string length and allocate a buffer, it is slightly slower, but the resulting String type is to be preferred.

  • The byte version of GetChars(Byte*, Int32, Char*, Int32) allows some fast techniques, particularly with multiple calls to large buffers. Bear in mind, however, that this method version is sometimes unsafe, since pointers are required.

  • If your app must convert a large amount of data, it should reuse the output buffer. In this case, the GetChars(Byte(), Int32, Int32, Char(), Int32) version that supports output character buffers is the best choice.

  • Consider using the Decoder.Convert method instead of GetCharCount. The conversion method converts as much data as possible and throws an exception if the output buffer is too small. For continuous decoding of a stream, this method is often the best choice.

The following example encodes a string into an array of bytes, and then decodes the bytes into an array of characters.

Imports System
Imports System.Text
Imports Microsoft.VisualBasic

Public Class SamplesEncoding   

   Public Shared Sub Main()

      ' Create two instances of UTF32Encoding: one with little-endian byte order and one with big-endian byte order. 
      Dim u32LE As Encoding = Encoding.GetEncoding("utf-32")
      Dim u32BE As Encoding = Encoding.GetEncoding("utf-32BE")

      ' Use a string containing the following characters: 
      '    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) 
      Dim myStr As String = "za" & ChrW(&H0306) & ChrW(&H01FD) & ChrW(&H03B2) 

      ' Encode the string using the big-endian byte order. 
      ' NOTE: In VB.NET, arrays contain one extra element by default. 
      '       The following line creates the array with the exact number of elements required. 
      Dim barrBE(u32BE.GetByteCount(myStr) - 1) As Byte
      u32BE.GetBytes(myStr, 0, myStr.Length, barrBE, 0)

      ' Encode the string using the little-endian byte order. 
      ' NOTE: In VB.NET, arrays contain one extra element by default. 
      '       The following line creates the array with the exact number of elements required. 
      Dim barrLE(u32LE.GetByteCount(myStr) - 1) As Byte
      u32LE.GetBytes(myStr, 0, myStr.Length, barrLE, 0)

      ' Get the char counts, and decode the byte arrays.
      Console.Write("BE array with BE encoding : ")
      PrintCountsAndChars(barrBE, u32BE)
      Console.Write("LE array with LE encoding : ")
      PrintCountsAndChars(barrLE, u32LE)

   End Sub 'Main


   Public Shared Sub PrintCountsAndChars(bytes() As Byte, enc As Encoding)

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

      ' Display the exact character count. 
      Dim iCC As Integer = enc.GetCharCount(bytes)
      Console.Write(" {0,-3}", iCC)

      ' Display the maximum character count. 
      Dim iMCC As Integer = enc.GetMaxCharCount(bytes.Length)
      Console.Write(" {0,-3} :", iMCC)

      ' Decode the bytes and display the characters. 
      Dim chars As Char() = enc.GetChars(bytes)
      Console.WriteLine(chars)

   End Sub 'PrintCountsAndChars 

End Class 'SamplesEncoding


'This code produces the following output.  The question marks take the place of characters that cannot be displayed at the console. 

'BE array with BE encoding : System.Text.UTF32Encoding : 5   12  :za??� 
'LE array with LE encoding : System.Text.UTF32Encoding : 5   12  :za??�

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.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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