Convert.FromBase64String Method (String)

 

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 static byte[] FromBase64String(
	string s
)

Parameters

s
Type: System.String

The string to convert.

Return Value

Type: System.Byte[]

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

Exception Condition
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.

System_CAPS_importantImportant

The FromBase64Stringmethod 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 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 sring.
       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 }

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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