Decoding a Base64-Encoded Binary -CodeIdol

Decoding a Base64-Encoded Binary

Problem

You have a String that contains information such as a bitmap encoded as base64. You need to decode this data (which may have been embedded in an email message) from a String into a byte[] so that you can access the original binary.

Solution

Using the static method Convert.FromBase64String on the Convert class, an encoded String may be decoded to its equivalent byte[]:

	using System;

	public static byte[] Base64DecodeString(string inputStr)
	{
	    byte[] decodedByteArray =
	      Convert.FromBase64String(inputStr);
	    
	    return (decodedByteArray);
	}

Discussion

The static FromBase64String method on the Convert class makes decoding an encoded base64 string a simple matter. This method returns a byte[] that contains the decoded elements of the String.

If you receive a file via email, such as an image file (.bmp), that has been converted to a string, you can convert it back into its original bitmap file, using something like the following:

	byte[] imageBytes = Base64DecodeString(bmpAsString);
	using (FileStream fstrm = new FileStream(@"C:\winnt_copy.bmp",
	                  FileMode.CreateNew, FileAccess.Write))
	{
	    using (BinaryWriter writer = new BinaryWriter(fstrm))
	    {
	         writer.Write(imageBytes);
	    }
	}

In this code, the bmpAsString variable was obtained from the code in the Discussion section of Recipe 2.11. The imageBytes byte[] is the bmpAsString String converted back to a byte[], which can then be written back to disk.

To encode a byte[] to a String, see Recipe 2.13.

April 16, 2009, 4:59 p.m.
posted by bert

Decoding a Base64-Encoded Binary