using System.IO;

using System.IO.Compression;

string sourceFile=@"D:\2.zip";

string destinationFile=@"D:\1.txt";

            private const long BUFFER_SIZE = 20480;

            // make sure the source file is there

            if (File.Exists ( sourceFile ))

            {

            FileStream sourceStream = null;

            FileStream destinationStream = null;

            GZipStream decompressedStream = null;

            byte[] quartetBuffer = null;

            try

            {

                // Read in the compressed source stream

                sourceStream = new FileStream ( sourceFile, FileMode.Open );

 

                // Create a compression stream pointing to the destiantion stream

                decompressedStream = new DeflateStream ( sourceStream, CompressionMode.Decompress, true );

 

                // Read the footer to determine the length of the destiantion file

                quartetBuffer = new byte[4];

                int position = (int)sourceStream.Length - 4;

                sourceStream.Position = position;

                sourceStream.Read ( quartetBuffer, 0, 4 );

                sourceStream.Position = 0;

                int checkLength = BitConverter.ToInt32 ( quartetBuffer, 0 );

 

                byte[] buffer = new byte[checkLength + 100];

 

                int offset = 0;

                int total = 0;

 

                // Read the compressed data into the buffer

                while ( true )

                {

                    int bytesRead = decompressedStream.Read ( buffer, offset, 100 );

 

                    if ( bytesRead == 0 )

                        break;

 

                    offset += bytesRead;

                    total += bytesRead;

                }

 

                // Now write everything to the destination file

                destinationStream = new FileStream ( destinationFile, FileMode.Create );

                destinationStream.Write ( buffer, 0, total );

 

                // and flush everyhting to clean out the buffer

                destinationStream.Flush ( );

            }

            catch ( ApplicationException ex )

            {

                Console.WriteLine(ex.Message, "解压文件时发生错误：");

            }

            finally

            {

                // Make sure we allways close all streams

                if ( sourceStream != null )

                    sourceStream.Close ( );

 

                if ( decompressedStream != null )

                    decompressedStream.Close ( );

 

                if ( destinationStream != null )

                    destinationStream.Close ( );

            }

            }