GZipStream Constructor (Stream, CompressionMode)


Initializes a new instance of the GZipStream class by using the specified stream and compression mode.

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

Public Sub New (
	stream As Stream,
	mode As CompressionMode


Type: System.IO.Stream

The stream the compressed or decompressed data is written to.

Type: System.IO.Compression.CompressionMode

One of the enumeration values that indicates whether to compress or decompress the stream.

Exception Condition

stream is null.


mode is not a valid CompressionMode enumeration value.


CompressionMode is Compress and CanWrite is false.


CompressionMode is Decompress and CanRead is false.

By default, GZipStream owns the underlying stream, so closing the stream parameter 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 GZipStream class is created with the mode parameter equal to Compress and no further action occurs, the stream will appear as a valid, empty compressed file.

By default, the compression level is set to Optimal when the compression mode is Compress.

The following example initializes a new instance of the GZipStream class with mode set to Compress. This example is part of a larger example provided for the GZipStream class.

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

    Private directoryPath As String = "c:\temp"
    Public Sub Main()
        Dim directorySelected As New DirectoryInfo(directoryPath)

        For Each fileToDecompress As FileInfo In directorySelected.GetFiles("*.gz")
    End Sub

    Public Sub Compress(directorySelected As DirectoryInfo)
        For Each fileToCompress As FileInfo In directorySelected.GetFiles()
            Using originalFileStream As FileStream = fileToCompress.OpenRead()
                If (File.GetAttributes(fileToCompress.FullName) And FileAttributes.Hidden) <> FileAttributes.Hidden And fileToCompress.Extension <> ".gz" Then
                    Using compressedFileStream As FileStream = File.Create(fileToCompress.FullName & ".gz")
                        Using compressionStream As New GZipStream(compressedFileStream, CompressionMode.Compress)

                        End Using
                    End Using
                    Dim info As New FileInfo(directoryPath & "\" & fileToCompress.Name & ".gz")
                    Console.WriteLine("Compressed {0} from {1} to {2} bytes.", fileToCompress.Name,
                                      fileToCompress.Length.ToString(), info.Length.ToString())

                End If
            End Using
    End Sub

    Private Sub Decompress(ByVal fileToDecompress As FileInfo)
        Using originalFileStream As FileStream = fileToDecompress.OpenRead()
            Dim currentFileName As String = fileToDecompress.FullName
            Dim newFileName = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length)

            Using decompressedFileStream As FileStream = File.Create(newFileName)
                Using decompressionStream As GZipStream = New GZipStream(originalFileStream, CompressionMode.Decompress)
                    Console.WriteLine("Decompressed: {0}", fileToDecompress.Name)
                End Using
            End Using
        End Using
    End Sub
End Module

Universal Windows Platform
Available since 8
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1
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