Read Method
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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)

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

Parameters

array
Type: System.Byte()
The array used to store decompressed bytes.
offset
Type: System.Int32
The byte offset in array at which the read bytes will be placed.
count
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.

ExceptionCondition
ArgumentNullException

array is Nothing.

InvalidOperationException

The CompressionMode value was Compress when the object was created.

- or -

The underlying stream does not support reading.

ArgumentOutOfRangeException

offset or count is less than zero.

-or-

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

InvalidDataException

The data is in an invalid format.

-or-

Decompression results in over 8 GB of data.

ObjectDisposedException

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.


Imports System.IO
Imports System.IO.Compression
Module Module1

    Sub Main()
        ' Path to directory of files to compress.
        Dim dirpath As String = "c:\users\public\reports"

        Dim di As DirectoryInfo = New DirectoryInfo(dirpath)


        ' Compress the directory's files.
        For Each fi As FileInfo In di.GetFiles()
            Compress(fi)
        Next

        ' Decompress all *.gz files in the directory.
        For Each fi As FileInfo In di.GetFiles("*.gz")
            Decompress(fi)
        Next

    End Sub

    ' Method to compress.
    Private Sub Compress(ByVal fi As FileInfo)
        ' Get the stream of the source file.
        Using inFile As FileStream = fi.OpenRead()
            ' Compressing:
            ' Prevent compressing hidden and already compressed files.

            If (File.GetAttributes(fi.FullName) And FileAttributes.Hidden) _
                <> FileAttributes.Hidden And fi.Extension <> ".gz" Then
                ' Create the compressed file.
                Using outFile As FileStream = File.Create(fi.FullName + ".gz")
                    Using Compress As GZipStream = _
                    	New GZipStream(outFile, CompressionMode.Compress)
                    	
                        ' Copy the source file into the compression stream.
                        inFile.CopyTo(Compress)

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

                    End Using
                End Using
            End If
        End Using
    End Sub

    ' Method to decompress.
    Private Sub Decompress(ByVal fi As FileInfo)
        ' Get the stream of the source file.
        Using inFile As FileStream = fi.OpenRead()
            ' Get orignial file extension, for example "doc" from report.doc.gz.
            Dim curFile As String = fi.FullName
            Dim origName = curFile.Remove(curFile.Length - fi.Extension.Length)

            ' Create the decompressed file.
            Using outFile As FileStream = File.Create(origName)
                Using Decompress As GZipStream = New GZipStream(inFile, _
                	CompressionMode.Decompress)
            		
  						' Copy the decompression stream 
                        ' into the output file.
            		    Decompress.CopyTo(outFile)

                    Console.WriteLine("Decompressed: {0}", fi.Name)

                End Using
            End Using
        End Using
    End Sub
End Module


.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.

Date

History

Reason

January 2012

Corrected exceptions.

Information enhancement.

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