Convert.FromBase64String(String) Method

Definition

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

public static byte[] FromBase64String (string s);

Parameters

s
String

The string to convert.

Returns

Byte[]

An array of 8-bit unsigned integers that is equivalent to s.

Exceptions

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.

Examples

The following example uses the ToBase64String(Byte[]) method to convert a byte array to a UUencoded (base-64) string, and then calls the FromBase64String(String) method to restore the original byte array.

using System;

public class Example
{
   public static void Main()
   {
       // Define a byte array.
       byte[] bytes = { 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 };
       Console.WriteLine("The byte array: ");
       Console.WriteLine("   {0}\n", BitConverter.ToString(bytes));

       // Convert the array to a base 64 string.
       string s = Convert.ToBase64String(bytes);
       Console.WriteLine("The base 64 string:\n   {0}\n", s);

       // Restore the byte array.
       byte[] newBytes = Convert.FromBase64String(s);
       Console.WriteLine("The restored byte array: ");
       Console.WriteLine("   {0}\n", BitConverter.ToString(newBytes));
   }
}
// The example displays the following output:
//     The byte array:
//        02-04-06-08-0A-0C-0E-10-12-14
//
//     The base 64 string:
//        AgQGCAoMDhASFA==
//
//     The restored byte array:
//        02-04-06-08-0A-0C-0E-10-12-14

The following is a more complex example that creates a 20-element array of 32-bit integers. It then uses the BitConverter.GetBytes(Int32) method to convert each element into a byte array, which it stores in the appropriate position in a buffer by calling the Array.Copy(Array, Int32, Array, Int32, Int32) method. This buffer is then passed to the ToBase64String(Byte[]) method to create a UUencoded (base-64) string. It then calls the FromBase64String(String) method to decode the UUencoded string, and calls the BitConverter.ToInt32 method to convert each set of four bytes (the size of a 32-bit integer) to an integer. The output from the example shows that the original array has been successfully restored.

using System;

public class Example
{
   public static void Main()
   {
      // Define an array of 20 elements and display it.
      int[] arr = new int[20];
      int value = 1;
      for (int ctr = 0; ctr <= arr.GetUpperBound(0); ctr++) {
         arr[ctr] = value;
         value = value * 2 + 1;
      }
      DisplayArray(arr);

      // Convert the array of integers to a byte array.
      byte[] bytes = new byte[arr.Length * 4];
      for (int ctr = 0; ctr < arr.Length; ctr++) {
         Array.Copy(BitConverter.GetBytes(arr[ctr]), 0,
                    bytes, ctr * 4, 4);
      }

      // Encode the byte array using Base64 encoding
      String base64 = Convert.ToBase64String(bytes);
      Console.WriteLine("The encoded string: ");
      for (int ctr = 0; ctr <= base64.Length / 50; ctr++)
         Console.WriteLine(base64.Substring(ctr * 50,
                                            ctr * 50 + 50 <= base64.Length
                                               ? 50 : base64.Length - ctr * 50));
      Console.WriteLine();

      // Convert the string back to a byte array.
      byte[] newBytes = Convert.FromBase64String(base64);

      // Convert the byte array back to an integer array.
      int[] newArr = new int[newBytes.Length/4];
      for (int ctr = 0; ctr < newBytes.Length / 4; ctr ++)
         newArr[ctr] = BitConverter.ToInt32(newBytes, ctr * 4);

      DisplayArray(newArr);
   }

   private static void DisplayArray(Array arr)
   {
      Console.WriteLine("The array:");
      Console.Write("{ ");
      for (int ctr = 0; ctr < arr.GetUpperBound(0); ctr++) {
         Console.Write("{0}, ", arr.GetValue(ctr));
         if ((ctr + 1) % 10 == 0)
            Console.Write("\n  ");
      }
      Console.WriteLine("{0} {1}", arr.GetValue(arr.GetUpperBound(0)), "}");
      Console.WriteLine();
   }
}
// The example displays the following output:
// The array:
// { 1, 3, 7, 15, 31, 63, 127, 255, 511, 1023,
//   2047, 4095, 8191, 16383, 32767, 65535, 131071, 262143, 524287, 1048575 }
//
// The encoded string:
// AQAAAAMAAAAHAAAADwAAAB8AAAA/AAAAfwAAAP8AAAD/AQAA/w
// MAAP8HAAD/DwAA/x8AAP8/AAD/fwAA//8AAP//AQD//wMA//8H
//
// The array:
// { 1, 3, 7, 15, 31, 63, 127, 255, 511, 1023,
//   2047, 4095, 8191, 16383, 32767, 65535, 131071, 262143, 524287, 1048575 }

Remarks

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

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.

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