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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)

[SecuritySafeCriticalAttribute]
public static byte[] FromBase64String(
	string s
)

Parameters

s
Type: System.String
A String.

Return Value

Type: System.Byte[]
An array of 8-bit unsigned integers equivalent to s.

ExceptionCondition
ArgumentNullException

s is null.

FormatException

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

-or-

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.

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 there isn't an integral number of 3-byte groups, the remaining bytes are effectively padded with zeroes 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 zeroes 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

using System;
class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      byte[] inArray = new byte[256];
      byte[] outArray = new byte[256];
      string s2;
      string s3;
      string step1 = "1) The input is a byte array (inArray) of arbitrary data.";
      string step2 = "2) Convert a subarray of the input data array to a base 64 string.";
      string step3 = "3) Convert the entire input data array to a base 64 string.";
      string step4 = "4) The two methods in steps 2 and 3 produce the same result?: {0}";
      string step5 = "5) Convert the base 64 string to an output byte array (outArray).";
      string step6 = "6) The input and output arrays, inArray and outArray, are equal?: {0}";
      int x;
      string nl = "\n";
      string ruler1a = "         1         2         3         4";
      string ruler2a = "1234567890123456789012345678901234567890";
      string ruler3a = "----+----+----+----+----+----+----+----+";
      string ruler1b = "         5         6         7      ";
      string ruler2b = "123456789012345678901234567890123456";
      string ruler3b = "----+----+----+----+----+----+----+-";
      string ruler = 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.

      outputBlock.Text += step1 + "\n";
      outputBlock.Text += "\n";
      for (x = 0; x < inArray.Length; x++)
      {
         inArray[x] = (byte)x;
         outputBlock.Text += String.Format("{0:X2} ", inArray[x]);
         if (((x + 1) % 20) == 0) outputBlock.Text += "\n";
      }
      outputBlock.Text += String.Format("{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.

      outputBlock.Text += step2 + "\n";
      s2 = Convert.ToBase64String(inArray, 0, inArray.Length);
      outputBlock.Text += String.Format("{0}{1}{2}{3}", nl, ruler, s2, nl) + "\n";

      // 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.

      outputBlock.Text += step3 + "\n";
      s3 = Convert.ToBase64String(inArray);

      // 4) Test whether the methods in steps 2 and 3 produce the same result.
      outputBlock.Text += String.Format(step4, s2.Equals(s3)) + "\n";

      // 5) Convert the base 64 string to an output array (outArray).
      outputBlock.Text += step5 + "\n";
      outArray = Convert.FromBase64String(s2);

      // 6) Is outArray equal to inArray?
      outputBlock.Text += String.Format(step6, ArraysAreEqual(inArray, outArray)) + "\n";
   }

   public static bool ArraysAreEqual(byte[] a1, byte[] a2)
   {
      if (a1.Length != a2.Length) return false;
      for (int i = 0; i < a1.Length; i++)
         if (a1[i] != a2[i]) return false;
      return true;
   }
}
/*
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
1234567890123456789012345678901234567890123456789012345678901234567890123456
----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+-
AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8gISIjJCUmJygpKissLS4vMDEyMzQ1Njc4
OTo7PD0+P0BBQkNERUZHSElKS0xNTk9QUVJTVFVWV1hZWltcXV5fYGFiY2RlZmdoaWprbG1ub3Bx
cnN0dXZ3eHl6e3x9fn+AgYKDhIWGh4iJiouMjY6PkJGSk5SVlpeYmZqbnJ2en6ChoqOkpaanqKmq
q6ytrq+wsbKztLW2t7i5uru8vb6/wMHCw8TFxsfIycrLzM3Oz9DR0tPU1dbX2Nna29zd3t/g4eLj
5OXm5+jp6uvs7e7v8PHy8/T19vf4+fr7/P3+/w==

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

*/


Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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