Encoding.GetChars Method (Byte(), Int32, Int32, Char(), Int32)


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When overridden in a derived class, decodes a sequence of bytes from the specified byte array into the specified character array.

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

Public MustOverride Function GetChars (
	bytes As Byte(),
	byteIndex As Integer,
	byteCount As Integer,
	chars As Char(),
	charIndex As Integer
) As Integer


Type: System.Byte()

The byte array containing the sequence of bytes to decode.

Type: System.Int32

The index of the first byte to decode.

Type: System.Int32

The number of bytes to decode.

Type: System.Char()

The character array to contain the resulting set of characters.

Type: System.Int32

The index at which to start writing the resulting set of characters.

Return Value

Type: System.Int32

The actual number of characters written into chars.

Exception Condition

bytes is null.


chars is null.


byteIndex or byteCount or charIndex is less than zero.


byteindex and byteCount do not denote a valid range in bytes.


charIndex is not a valid index in chars.


chars does not have enough capacity from charIndex to the end of the array to accommodate the resulting characters.


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


DecoderFallback is set to DecoderExceptionFallback.

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

Encoding.GetChars gets characters from an input byte sequence. Encoding.GetChars is different than Decoder.GetChars because Encoding expects discrete conversions, while Decoder is designed for multiple passes on a single input stream.

If the data to be converted is available only in sequential blocks (such as data read from a stream) or if the amount of data is so large that it needs to be divided into smaller blocks, you should use the Decoder or the Encoder provided by the GetDecoder method or the GetEncoder method, respectively, of a derived class.

Note    This method is intended to operate on Unicode characters, not on arbitrary binary data, such as byte arrays. If you need to encode arbitrary binary data into text, you should use a protocol such as uuencode, which is implemented by methods such as Convert.ToBase64CharArray.

The GetCharCount method determines how many characters result in decoding a sequence of bytes, and the GetChars 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, because byte sequences can be interrupted when processed in batches. (For example, part of an ISO-2022 shift sequence may end one GetChars call and continue at the beginning of the next GetChars call. Encoding.GetChars will call the fallback for those incomplete sequences, but Decoder will remember those sequences for the next call.)

  • If your app handles string outputs, the GetString method is recommended. 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 converts a string from one encoding to another.

Imports System.Text

Class Example
   Shared Sub Main()
      Dim unicodeString As String = "This string contains the unicode character Pi (" & ChrW(&H03A0) & ")"

      ' Create two different encodings.
      Dim ascii As Encoding = Encoding.ASCII
      Dim unicode As Encoding = Encoding.Unicode

      ' Convert the string into a byte array.
      Dim unicodeBytes As Byte() = unicode.GetBytes(unicodeString)

      ' Perform the conversion from one encoding to the other.
      Dim asciiBytes As Byte() = Encoding.Convert(unicode, ascii, unicodeBytes)

      ' Convert the new byte array into a char array and then into a string.
      Dim asciiChars(ascii.GetCharCount(asciiBytes, 0, asciiBytes.Length)-1) As Char
      ascii.GetChars(asciiBytes, 0, asciiBytes.Length, asciiChars, 0)
      Dim asciiString As New String(asciiChars)

      ' Display the strings created before and after the conversion.
      Console.WriteLine("Original string: {0}", unicodeString)
      Console.WriteLine("Ascii converted string: {0}", asciiString)
   End Sub
End Class
' The example displays the following output:
'    Original string: This string contains the unicode character Pi (Π)
'    Ascii converted string: This string contains the unicode character Pi (?)

The following example encodes a string into an array of bytes, and then decodes a range of 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 barrBE 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 barrLE 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, decode eight bytes starting at index 0,
      ' and print out the counts and the resulting bytes.
      Console.Write("BE array with BE encoding : ")
      PrintCountsAndChars(barrBE, 0, 8, u32BE)
      Console.Write("LE array with LE encoding : ")
      PrintCountsAndChars(barrLE, 0, 8, u32LE)

   End Sub 'Main

   Public Shared Sub PrintCountsAndChars(bytes() As Byte, index As Integer, count As Integer, 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, index, count)
      Console.Write(" {0,-3}", iCC)

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

      ' Decode the bytes.
      Dim chars As Char() = enc.GetChars(bytes, index, count)

      ' The following is an alternative way to decode the bytes:
      ' 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 chars(iCC - 1) As Char
      ' enc.GetChars( bytes, index, count, chars, 0 )

      ' Display the characters.

   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 : 2   6   :za
'LE array with LE encoding : System.Text.UTF32Encoding : 2   6   :za

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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