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GZipStream.EndRead Method

Waits for the pending asynchronous read to complete.

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

public override int EndRead(
	IAsyncResult asyncResult


Type: System.IAsyncResult
The reference to the pending asynchronous request to finish.

Return Value

Type: System.Int32
The number of bytes read from the stream, between zero (0) and the number of bytes you requested. GZipStream returns zero (0) only at the end of the stream; otherwise, it blocks until at least one byte is available.


asyncResult is null.


asyncResult did not originate from a BeginRead method on the current stream.


The end operation cannot be performed because the stream is closed.

Call this method to determine how many bytes were read from the stream. This method can be called once to return the amount of bytes read between calls to BeginRead and EndRead.

This method blocks until the I/O operation has completed.

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

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

namespace zip

    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 *.gz files in the directory.
            foreach (FileInfo fi in di.GetFiles("*.gz"))



        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 != ".gz")
                    // Create the compressed file.
                    using (FileStream outFile = 
                    			File.Create(fi.FullName + ".gz"))
                        using (GZipStream Compress = 
                        	new GZipStream(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.gz.
                string curFile = fi.FullName;
                string origName = curFile.Remove(curFile.Length - 

                //Create the decompressed file.
                using (FileStream outFile = File.Create(origName))
                    using (GZipStream Decompress = new GZipStream(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.