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Convert.FromBase64String Method

Converts the specified string, which encodes binary data as base-64 digits, to an equivalent 8-bit unsigned integer array.

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

Public Shared Function FromBase64String ( _
	s As String _
) As Byte()


Type: System.String
The string to convert.

Return Value

Type: System.Byte()
An array of 8-bit unsigned integers that is equivalent to s.


s is Nothing.


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


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

s 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 s because all white-space characters are ignored.

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

Important noteImportant

The FromBase64String method is designed to process a single string 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 FromBase64String method to decode UUencoded (base-64) data and save it as binary output.

Public Sub DecodeWithString()
   Dim inFile As System.IO.StreamReader
   Dim base64String As String

      Dim base64CharArray() As Char
      inFile = New System.IO.StreamReader(inputFileName, _
      base64CharArray = New Char(inFile.BaseStream.Length) {}
      inFile.Read(base64CharArray, 0, inFile.BaseStream.Length)
      base64String = New String(base64CharArray, _
                                0, _
                                base64CharArray.Length - 1)
   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.FromBase64String(base64String)
   Catch exp As System.ArgumentNullException
      System.Console.WriteLine("Base 64 string is null.")
   Catch exp As System.FormatException
      System.Console.WriteLine("Base 64 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 ToBase64String and FromBase64String 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.ToBase64String() and 
'                               Convert.FromBase64String() methods
Class Sample
   Public Shared Sub Main()
      Dim inArray(255)  As Byte
      Dim outArray(255) As Byte
      Dim s2 As String
      Dim s3 As String
      Dim step1 As String = "1) The input is a byte array (inArray) of arbitrary data."
      Dim step2 As String = "2) Convert a subarray of the input data array to a base 64 string."
      Dim step3 As String = "3) Convert the entire input data array to a base 64 string."
      Dim step4 As String = "4) The two methods in steps 2 and 3 produce the same result: {0}"
      Dim step5 As String = "5) Convert the base 64 string to an output byte array (outArray)."
      Dim step6 As String = "6) The input and output arrays, inArray and outArray, are equal: {0}"
      Dim x 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, nl)

      ' 1) Display an arbitrary array of input data (inArray). The data could be 
      '    derived from user input, a file, an algorithm, etc.
      For x = 0 To inArray.Length - 1
         inArray(x) = CByte(x)
         Console.Write("{0:X2} ", inArray(x))
         If (x + 1) Mod 20 = 0 Then
         End If
      Next x
      Console.Write("{0}{0}", nl)

      ' 2) Convert a subarray of the input data to a base64 string. In this case, 
      '    the subarray is the entire input data array. New lines (CRLF) are inserted.
      s2 = Convert.ToBase64String(inArray, 0, inArray.Length, _
      Console.WriteLine("{0}{1}{2}{3}", nl, ruler, s2, nl)

      ' 3) Convert the input data to a base64 string. In this case, the entire 
      '    input data array is converted by default. New lines (CRLF) are inserted.
      s3 = Convert.ToBase64String(inArray, Base64FormattingOptions.InsertLineBreaks)

      ' 4) Test whether the methods in steps 2 and 3 produce the same result.
      Console.WriteLine(step4, s2.Equals(s3))

      ' 5) Convert the base 64 string to an output array (outArray).
      outArray = Convert.FromBase64String(s2)

      ' 6) Is outArray equal to inArray?
      Console.WriteLine(step6, ArraysAreEqual(inArray, outArray))
   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) The input is a byte array (inArray) 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 a subarray of the input data array to a base 64 string.
'         1         2         3         4         5         6         7
'3) Convert the entire input data array to a base 64 string.
'4) The two methods in steps 2 and 3 produce the same result: True
'5) Convert the base 64 string to an output byte array (outArray).
'6) The input and output arrays, inArray and outArray, are equal: True

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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