If the data to be converted is available only in sequential blocks (such as data read from a stream) or if the amount of data is so large that it needs to be divided into smaller blocks, you should use the Decoder object returned by the GetDecoder method of a derived class.

See the Remarks section of the Encoding.GetChars reference topic for a discussion of decoding techniques and considerations.

Note that the precise behavior of the GetString method for a particular Encoding implementation depends on the fallback strategy defined for that Encoding object. For more information, see the "Choosing a Fallback Strategy" section of the Character Encoding in the .NET Framework topic.

The following example reads a UTF-8 encoded string from a binary file represented by a FileStream object. For files that are smaller than 2,048 bytes, it reads the contents of the entire file into a byte array and calls the GetString(Byte[]) method to perform the decoding. For larger files, it reads 2,048 bytes at a time into a byte array, calls the Decoder.GetCharCount(Byte[], Int32, Int32) method to determine how many characters are contained in the array, and then calls the Decoder.GetChars(Byte[], Int32, Int32, Char[], Int32) method to perform the decoding.

This is a UTF-8-encoded file that contains primarily Latin text, although it
does list the first twelve letters of the Russian (Cyrillic) alphabet:
А б в г д е ё ж з и й к
The goal is to save this file, then open and decode it as a binary stream.