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DeflateStream Constructor (Stream, CompressionMode, Boolean)

Initializes a new instance of the DeflateStream class using the specified stream and CompressionMode value, and a value that specifies whether to leave the stream open.

Namespace:  System.IO.Compression
Assembly:  System (in System.dll)

public DeflateStream(
	Stream stream,
	CompressionMode mode,
	bool leaveOpen


Type: System.IO.Stream
The stream to compress or decompress.
Type: System.IO.Compression.CompressionMode
One of the CompressionMode values that indicates the action to take.
Type: System.Boolean
true to leave the stream open; otherwise, false.


stream is null.


mode is not a valid CompressionMode value.


CompressionMode is Compress and CanWrite is false.


CompressionMode is Decompress and CanRead is false.

By default, DeflateStream owns the underlying stream, so closing the stream also closes the underlying stream. Note that the state of the underlying stream can affect the usability of the stream. Also, no explicit checks are performed, so no additional exceptions are thrown when the new instance is created.

If an instance of the DeflateStream class is created with the mode parameter equal to Compress, header information is inserted immediately. If no further action occurs, the stream appears as a valid, empty, compressed file.

Using the DeflateStream class to compress a file larger than 4 GB raises an exception.

The following code example shows how to use the DeflateStream class to compress and decompress a file.

using System;
using System.IO;
using System.IO.Compression;

public class Program

    public static void Main()
        // Path to directory of files to compress and decompress.
        string dirpath = @"c:\users\public\reports";

        DirectoryInfo di = new DirectoryInfo(dirpath);

        // Compress the directory's files.
        foreach (FileInfo fi in di.GetFiles())

        // Decompress all *.cmp files in the directory.
        foreach (FileInfo fi in di.GetFiles("*.cmp"))


    public static void Compress(FileInfo fi)
        // Get the stream of the source file.
        using (FileStream inFile = fi.OpenRead())
            // Prevent compressing hidden and already compressed files.
            if ((File.GetAttributes(fi.FullName) & FileAttributes.Hidden)
                != FileAttributes.Hidden & fi.Extension != ".cmp")
                // Create the compressed file.
                using (FileStream outFile = 
                        File.Create(fi.FullName + ".cmp"))
                    using (DeflateStream Compress = 
                        new DeflateStream(outFile, 
                        // Copy the source file into 
                        // the compression stream.

                        Console.WriteLine("Compressed {0} from {1} to {2} bytes.",
                        fi.Name, fi.Length.ToString(), outFile.Length.ToString());

    public static void Decompress(FileInfo fi)
        // Get the stream of the source file.
        using (FileStream inFile = fi.OpenRead())
        	// Get original file extension, 
            // for example "doc" from report.doc.cmp.
        	string curFile = fi.FullName;
        	string origName = curFile.Remove(curFile.Length 
                    - fi.Extension.Length);

        	//Create the decompressed file.
        	using (FileStream outFile = File.Create(origName))
        	    using (DeflateStream Decompress = new DeflateStream(inFile,
                        // Copy the decompression stream 
                        // into the output file.
            		Console.WriteLine("Decompressed: {0}", fi.Name);

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.