Convert.FromBase64CharArray Method (Char(), Int32, Int32)


The .NET API Reference documentation has a new home. Visit the .NET API Browser on to see the new experience.

Converts a subset of a Unicode character array, which encodes binary data as base-64 digits, to an equivalent 8-bit unsigned integer array. Parameters specify the subset in the input array and the number of elements to convert.

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

Public Shared Function FromBase64CharArray (
	inArray As Char(),
	offset As Integer,
	length As Integer
) As Byte()


Type: System.Char()

A Unicode character array.

Type: System.Int32

A position within inArray.

Type: System.Int32

The number of elements in inArray to convert.

Return Value

Type: System.Byte()

An array of 8-bit unsigned integers equivalent to length elements at position offset in inArray.

Exception Condition

inArray is null.


offset or length is less than 0.


offset plus length indicates a position not within inArray.


The length of inArray, ignoring white-space characters, is not zero or a multiple of 4.


The format of inArray is invalid. inArray contains a non-base-64 character, more than two padding characters, or a non-white-space character among the padding characters.

inArray is composed of base-64 digits, white-space characters, and trailing padding characters. The base-64 digits in ascending order from zero are the uppercase characters "A" to "Z", lowercase characters "a" to "z", numerals "0" to "9", and the symbols "+" and "/".

The white-space characters, and their Unicode names and hexadecimal code points, are tab (CHARACTER TABULATION, U+0009), newline (LINE FEED, U+000A), carriage return (CARRIAGE RETURN, U+000D), and blank (SPACE, U+0020). An arbitrary number of white-space characters can appear in inArray because all white-space characters are ignored.

The valueless character, "=", is used for trailing padding. The end of inArray can consist of zero, one, or two padding characters.


The FromBase64CharArray method is designed to process a single character array that contains all the data to be decoded. To decode base-64 character data from a stream, use the System.Security.Cryptography.FromBase64Transform class.

The following example demonstrates the use of the FromBase64CharArray(Char(), Int32, Int32) method to decode UUencoded (base-64) data and save it as binary output.

Public Sub DecodeWithCharArray()
   Dim inFile As System.IO.StreamReader
   Dim base64CharArray() As Char

      inFile = New System.IO.StreamReader(inputFileName, _

      ReDim base64CharArray(inFile.BaseStream.Length - 1)
      inFile.Read(base64CharArray, 0, inFile.BaseStream.Length)
   Catch exp As System.Exception
      ' Error creating stream or reading from it.
      System.Console.WriteLine("{0}", exp.Message)
   End Try

   ' Convert the Base64 UUEncoded input into binary output.
   Dim binaryData() As Byte
      binaryData = System.Convert.FromBase64CharArray(base64CharArray, 0, _
   Catch exp As System.ArgumentNullException
      System.Console.WriteLine("Base 64 character array is null.")
   Catch exp As System.FormatException
      System.Console.WriteLine("Base 64 Char Array length is not " + _
               "4 or is not an even multiple of 4")
   End Try

   ' Write out the decoded data.
   Dim outFile As System.IO.FileStream
      outFile = New System.IO.FileStream(outputFileName, _
                                         System.IO.FileMode.Create, _
      outFile.Write(binaryData, 0, binaryData.Length - 1)
   Catch exp As System.Exception
      ' Error creating stream or writing to it.
      System.Console.WriteLine("{0}", exp.Message)
   End Try
End Sub

The following example demonstrates the ToBase64CharArray(Byte(), Int32, Int32, Char(), Int32, Base64FormattingOptions) and FromBase64CharArray(Char(), Int32, Int32) methods. The input is divided into groups of three bytes (24 bits) each. Consequently, each group consists of four 6-bit numbers where each number ranges from decimal 0 to 63. In this example, there are 85 3-byte groups with one byte remaining. The first group consists of the hexadecimal values 00, 01, and 02, which yield four 6-bit values equal to decimal 0, 0, 4, and 2. Those four values correspond to the base-64 digits, "A", "A", "E", and "C", at the beginning of the output.

If an integral number of 3-byte groups does not exist, the remaining bytes are effectively padded with zeros to form a complete group. In this example, the value of the last byte is hexadecimal FF. The first 6 bits are equal to decimal 63, which corresponds to the base-64 digit "/" at the end of the output, and the next 2 bits are padded with zeros to yield decimal 48, which corresponds to the base-64 digit, "w". The last two 6-bit values are padding and correspond to the valueless padding character, "=".

' This example demonstrates the Convert.ToBase64CharArray() and 
'                               Convert.FromBase64CharArray methods
Class Sample
   Public Shared Sub Main()
      Dim byteArray1(255) As Byte
      Dim byteArray2(255) As Byte
      Dim charArray(351) As Char
      Dim charArrayLength As Integer
      Dim nl As String = Environment.NewLine

      Dim ruler1a As String = "         1         2         3         4"
      Dim ruler2a As String = "1234567890123456789012345678901234567890"
      Dim ruler3a As String = "----+----+----+----+----+----+----+----+"
      Dim ruler1b As String = "         5         6         7      "
      Dim ruler2b As String = "123456789012345678901234567890123456"
      Dim ruler3b As String = "----+----+----+----+----+----+----+-"
      Dim ruler As String = String.Concat(ruler1a, ruler1b, nl, _
                                          ruler2a, ruler2b, nl, _
                                          ruler3a, ruler3b)

      ' 1) Initialize and display a Byte array of arbitrary data.
      Console.WriteLine("1) Input: A Byte array of arbitrary data.{0}", nl)
      Dim x As Integer
      For x = 0 To byteArray1.Length - 1
         byteArray1(x) = CByte(x)
         Console.Write("{0:X2} ", byteArray1(x))
         If(x + 1) Mod 20 = 0 Then
         End If
      Next x
      Console.Write("{0}{0}", nl)

      ' 2) Convert the input Byte array to a Char array, with newlines inserted.
      charArrayLength = Convert.ToBase64CharArray( _
                                byteArray1, 0, byteArray1.Length, _
                                charArray, 0, _
      Console.WriteLine("2) Convert the input Byte array to a Char array with newlines.")
      Console.Write("   Output: A Char array (length = {0}). ", charArrayLength)
      Console.WriteLine("The elements of the array are:{0}", nl)
      Console.WriteLine(New [String](charArray))

      ' 3) Convert the Char array back to a Byte array.
      Console.WriteLine("3) Convert the Char array to an output Byte array.")
      byteArray2 = Convert.FromBase64CharArray(charArray, 0, charArrayLength)

      ' 4) Are the input and output Byte arrays equivalent?
      Console.WriteLine("4) The output Byte array is equal to the input Byte array: {0}", _
                            ArraysAreEqual(byteArray1, byteArray2))
   End Sub 'Main

   Public Shared Function ArraysAreEqual(a1() As Byte, a2() As Byte) As Boolean
      If a1.Length <> a2.Length Then
         Return False
      End If
      Dim i As Integer
      For i = 0 To a1.Length - 1
         If a1(i) <> a2(i) Then
            Return False
         End If
      Next i
      Return True
   End Function 'ArraysAreEqual
End Class 'Sample
'This example produces the following results:
'1) Input: A Byte array of arbitrary data.
'00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13
'14 15 16 17 18 19 1A 1B 1C 1D 1E 1F 20 21 22 23 24 25 26 27
'28 29 2A 2B 2C 2D 2E 2F 30 31 32 33 34 35 36 37 38 39 3A 3B
'3C 3D 3E 3F 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4F
'50 51 52 53 54 55 56 57 58 59 5A 5B 5C 5D 5E 5F 60 61 62 63
'64 65 66 67 68 69 6A 6B 6C 6D 6E 6F 70 71 72 73 74 75 76 77
'78 79 7A 7B 7C 7D 7E 7F 80 81 82 83 84 85 86 87 88 89 8A 8B
'8C 8D 8E 8F 90 91 92 93 94 95 96 97 98 99 9A 9B 9C 9D 9E 9F
'A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 AA AB AC AD AE AF B0 B1 B2 B3
'B4 B5 B6 B7 B8 B9 BA BB BC BD BE BF C0 C1 C2 C3 C4 C5 C6 C7
'C8 C9 CA CB CC CD CE CF D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 DA DB
'DC DD DE DF E0 E1 E2 E3 E4 E5 E6 E7 E8 E9 EA EB EC ED EE EF
'F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF
'2) Convert the input Byte array to a Char array with newlines.
'   Output: A Char array (length = 352). The elements of the array are:
'         1         2         3         4         5         6         7
'3) Convert the Char array to an output Byte array.
'4) The output Byte array is equal to the input Byte array: True

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
Return to top