using (FileStream target = new FileStream(zipFilename, FileMode.Create, FileAccess.Write))
using (GZipStream alg = new GZipStream(target, CompressionMode.Compress))
{
byte[] data = File.ReadAllBytes(fileToBeCompressed);
alg.Write(data, 0, data.Length);
alg.Flush();
}

Code explanation:

If you are going to compress a file then you must specify the CompressionMode.Compress option, and also you must specify a Stream that will the data be written to.

After creating the class you can compress the data by using its Write() method.

If you intended to use the Deflate algorithm, just change the class name to DeflateStream.

Decompressing a file

The code that decompresses a compressed file is very similar:

string compressedFile = "D:\\CompressedGreatDocument.zip";
string originalFileName = "D:\\My Great Word Document.doc";

using (FileStream zipFile = new FileStream(compressedFile, FileMode.Open, FileAccess.Read))
using (FileStream originalFile = new FileStream(originalFileName, FileMode.Create, FileAccess.Write))
using (GZipStream alg = new GZipStream(zipFile, CompressionMode.Decompress))
{
while (true)
{
// Reading 100bytes by 100bytes
byte[] buffer = new byte[100];
// The Read() method returns the number of bytes read
int bytesRead = alg.Read(buffer, 0, buffer.Length);

originalFile.Write(buffer, 0, returnedBytes);

if (bytesRead != buffer.Length)
break;
}
}

Code explanation:

First, we create a file stream to read the ZIP file, and then we created our algorithm class that encapsulates the file stream for decompressing it.

Then we created a file stream for the original file, for writing the decompressed data.

After that, we read the data compressed 100bytes after each other -you may prefer more- and write this data to the original file stream.

By encapsulating disposable objects into using statements you become assured that every object will be disposed in a certain point -end of the using statement- and no object will retain in memory.

Try it Yourself

Develop a simple application that can be used to compress and decompress files. This application can compress several files into one file and decompress them as well.

Besides algorithms classes you may use System.IO.BinaryWriter and System.IO.BinaryReader to get full control of how the file contents will be.