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How to: Compress Files 

Use the GZipStream class to compress and decompress data. The following code example creates a file (test.txt) in the current directory, fills it with text, and displays the contents of the file to the console. The code then uses the GZipStream class to create a compressed version of the file (test.txt.gz) and compares the size of the two files. Finally, the code reads in the compressed file, decompresses it, and writes out a new file (test.txt.gz.txt) to the current directory. The code then displays the contents of the decompressed file.

You can also use the DeflateStream class to compress and decompress data.


using System;
using System.Collections.Generic;
using System.IO;
using System.IO.Compression;

public class CompressionSnippet
    public static void Main()
        string path = "test.txt";

        // Create the text file if it doesn't already exist.
        if (!File.Exists(path))
            Console.WriteLine("Creating a new test.txt file");
            string[] text = new string[] {"This is a test text file.",
                "This file will be compressed and written to the disk.",
                "Once the file is written, it can be decompressed",
                "using various compression tools.",
                "The GZipStream and DeflateStream class use the same",
                "compression algorithms, the primary difference is that",
                "the GZipStream class includes a cyclic redundancy check",
                "that can be useful for detecting data corruption.",
                "One other side note: both the GZipStream and DeflateStream",
                "classes operate on streams as opposed to file-based",
                "compression; data is read on a byte-by-byte basis, so it",
                "is not possible to perform multiple passes to determine the",
                "best compression method. Already compressed data can actually",
                "increase in size if compressed with these classes."};

            File.WriteAllLines(path, text);

        Console.WriteLine("Contents of {0}", path);


        UncompressFile(path + ".gz");

        Console.WriteLine("Contents of {0}", path + ".gz.txt");
        Console.WriteLine(File.ReadAllText(path + ".gz.txt"));


    public static void CompressFile(string path)
        FileStream sourceFile = File.OpenRead(path);
        FileStream destinationFile = File.Create(path + ".gz");

        byte[] buffer = new byte[sourceFile.Length];
        sourceFile.Read(buffer, 0, buffer.Length);

        using (GZipStream output = new GZipStream(destinationFile,
            Console.WriteLine("Compressing {0} to {1}.", sourceFile.Name,
                destinationFile.Name, false);

            output.Write(buffer, 0, buffer.Length);

        // Close the files.

    public static void UncompressFile(string path)
        FileStream sourceFile = File.OpenRead(path);
        FileStream destinationFile = File.Create(path + ".txt");

        // Because the uncompressed size of the file is unknown, 
        // we are using an arbitrary buffer size.
        byte[] buffer = new byte[4096];
        int n;

        using (GZipStream input = new GZipStream(sourceFile,
            CompressionMode.Decompress, false))
            Console.WriteLine("Decompressing {0} to {1}.", sourceFile.Name,

            n = input.Read(buffer, 0, buffer.Length);
            destinationFile.Write(buffer, 0, n);

        // Close the files.

See Also

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