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

Definition

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.

public static byte[] FromBase64CharArray (char[] inArray, int offset, int length);

Parameters

inArray
Char[]

A Unicode character array.

offset
Int32

A position within inArray.

length
Int32

The number of elements in inArray to convert.

Returns

Byte[]

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

Exceptions

inArray is null.

offset or length is less than 0.

-or-

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.

-or-

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.

Examples

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 void DecodeWithCharArray() {
   System.IO.StreamReader inFile;
   char[] base64CharArray;

   try {
      inFile = new System.IO.StreamReader(inputFileName,
                              System.Text.Encoding.ASCII);
      base64CharArray = new char[inFile.BaseStream.Length];
      inFile.Read(base64CharArray, 0, (int)inFile.BaseStream.Length);
      inFile.Close();
   }
   catch (System.Exception exp) {
      // Error creating stream or reading from it.
      System.Console.WriteLine("{0}", exp.Message);
      return;
   }

   // Convert the Base64 UUEncoded input into binary output.
   byte[] binaryData;
   try {
      binaryData =
         System.Convert.FromBase64CharArray(base64CharArray,
                                    0,
                                    base64CharArray.Length);
   }
   catch ( System.ArgumentNullException ) {
      System.Console.WriteLine("Base 64 character array is null.");
      return;
   }
   catch ( System.FormatException ) {
      System.Console.WriteLine("Base 64 Char Array length is not " +
         "4 or is not an even multiple of 4." );
      return;
   }

   // Write out the decoded data.
   System.IO.FileStream outFile;
   try {
      outFile = new System.IO.FileStream(outputFileName,
                                 System.IO.FileMode.Create,
                                 System.IO.FileAccess.Write);
      outFile.Write(binaryData, 0, binaryData.Length);
      outFile.Close();
   }
   catch (System.Exception exp) {
      // Error creating stream or writing to it.
      System.Console.WriteLine("{0}", exp.Message);
   }
}

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

using System;

class Sample
{
    public static void Main()
    {
    byte[] byteArray1 = new byte[256];
    byte[] byteArray2 = new byte[256];
    char[] charArray  = new char[352];
    int charArrayLength;
    string nl = Environment.NewLine;

    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);

// 1) Initialize and display a Byte array of arbitrary data.
    Console.WriteLine("1) Input: A Byte array of arbitrary data.{0}", nl);
    for (int x = 0; x < byteArray1.Length; x++)
    {
    byteArray1[x] = (byte)x;
    Console.Write("{0:X2} ", byteArray1[x]);
    if (((x+1)%20) == 0) Console.WriteLine();
    }
    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, Base64FormattingOptions.InsertLineBreaks);
    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(ruler);
    Console.WriteLine(new String(charArray));
    Console.WriteLine();

// 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));
    }

    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) 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
1234567890123456789012345678901234567890123456789012345678901234567890123456
----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+-
AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8gISIjJCUmJygpKissLS4vMDEyMzQ1Njc4
OTo7PD0+P0BBQkNERUZHSElKS0xNTk9QUVJTVFVWV1hZWltcXV5fYGFiY2RlZmdoaWprbG1ub3Bx
cnN0dXZ3eHl6e3x9fn+AgYKDhIWGh4iJiouMjY6PkJGSk5SVlpeYmZqbnJ2en6ChoqOkpaanqKmq
q6ytrq+wsbKztLW2t7i5uru8vb6/wMHCw8TFxsfIycrLzM3Oz9DR0tPU1dbX2Nna29zd3t/g4eLj
5OXm5+jp6uvs7e7v8PHy8/T19vf4+fr7/P3+/w==

3) Convert the Char array to an output Byte array.
4) The output Byte array is equal to the input Byte array: True

*/

Remarks

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.

Important

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.

Applies to

Product Versions
.NET Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9
.NET Framework 1.1, 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1
.NET Standard 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 2.0, 2.1
UWP 10.0

See also