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GZipStream.Read Method

Updated: January 2012

Reads a number of decompressed bytes into the specified byte array.

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

public override int Read(
	byte[] array,
	int offset,
	int count


Type: System.Byte[]
The array used to store decompressed bytes.
Type: System.Int32
The byte offset in array at which the read bytes will be placed.
Type: System.Int32
The maximum number of decompressed bytes to read.

Return Value

Type: System.Int32
The number of bytes that were decompressed into the byte array. If the end of the stream has been reached, zero or the number of bytes read is returned.


array is null.


The CompressionMode value was Compress when the object was created.

- or -

The underlying stream does not support reading.


offset or count is less than zero.


array length minus the index starting point is less than count.


The data is in an invalid format.


Decompression results in over 8 GB of data.


The stream is closed.

If data is found in an invalid format, an InvalidDataException is thrown as one of the last operations. A cyclic redundancy check (CRC) is performed as one of the last operations of this method.

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.




January 2012

Corrected exceptions.

Information enhancement.

Community Additions

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