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GZipStream.Read Method

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

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

Public Overrides Function Read ( _
	array As Byte(), _
	offset As Integer, _
	count As Integer _
) As Integer


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 Nothing.


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.


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 example shows how to compress and decompress bytes by using the Read and Write methods.

Imports System.IO
Imports System.IO.Compression
Imports System.Text

Module Module1

    Sub Main()
        Dim uniEncode As UnicodeEncoding = New UnicodeEncoding()

        Dim bytesToCompress = uniEncode.GetBytes("example text to compress and decompress")
        Console.WriteLine("starting with: " + uniEncode.GetString(bytesToCompress))

        Using fileToCompress As FileStream = File.Create("examplefile.gz")
            Using compressionStream As GZipStream = New GZipStream(fileToCompress, CompressionMode.Compress)
                compressionStream.Write(bytesToCompress, 0, bytesToCompress.Length)
            End Using 
        End Using 

        Dim decompressedBytes(bytesToCompress.Length - 1) As Byte 
        Using fileToDecompress As FileStream = File.Open("examplefile.gz", FileMode.Open)
            Using decompressionStream As GZipStream = New GZipStream(fileToDecompress, CompressionMode.Decompress)
                decompressionStream.Read(decompressedBytes, 0, bytesToCompress.Length)
            End Using 
        End Using

        Console.WriteLine("ending with: " + uniEncode.GetString(decompressedBytes))
    End Sub 
End Module

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1
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