C# GZipStream Example (DeflateStream)

This C# example program uses GZipStream to compress a file. It requires System.IO.Compression.
GZipStream. This class compresses data. It saves data efficiently—such as in compressed log files. GZIP has a file header, while DEFLATE does not.Compress Data
We develop a utility method in the C# language that uses the System.IO.Compression namespace. It creates GZIP files. It writes them to the disk.
GZipStream example. We use the .NET Framework's built-in methods. Compression and decompression using GZIP is common in any programming language. GZIP is widely used on the Internet.

Note: The GZIP compression algorithm is used on many web pages to boost performance. This method shows the use of GZIP on a string.


Part A: We use Path.GetTempFileName and File.WriteAllText. This writes the string to a temporary file.

Part B: We use FileStream here to read in bytes from the file. The using statement provides effective system resource disposal.

UsingByte Array

Part C: We use a new GZipStream to write the compressed data to the disk. We must combine it with a FileStream.

C# program that compresses using System.IO; using System.IO.Compression; using System.Text; class Program { static void Main() { try { // 1. // Starting file is 26,747 bytes. string anyString = File.ReadAllText("TextFile1.txt"); // 2. // Output file is 7,388 bytes. CompressStringToFile("new.gz", anyString); } catch { // Could not compress. } } public static void CompressStringToFile(string fileName, string value) { // A. // Write string to temporary file. string temp = Path.GetTempFileName(); File.WriteAllText(temp, value); // B. // Read file into byte array buffer. byte[] b; using (FileStream f = new FileStream(temp, FileMode.Open)) { b = new byte[f.Length]; f.Read(b, 0, (int)f.Length); } // C. // Use GZipStream to write compressed bytes to target file. using (FileStream f2 = new FileStream(fileName, FileMode.Create)) using (GZipStream gz = new GZipStream(f2, CompressionMode.Compress, false)) { gz.Write(b, 0, b.Length); } } } Output Starting file is 26,747 bytes. Output file is 7,388 bytes.
Notes, reliable. CompressStringToFile is tested and reliable. I have used it in deployed applications. It however can be slow—caching, or other optimizations may be needed.Memoization

Note: This article used to have an example that was incorrect. It had an encoding problem. Jon wrote in with a fix.

DeflateStream. With DeflateStream we can output a deflate file. A GZIP file contains a DEFLATE body. With GZIP we have an additional header.

So: We can use DeflateStream to generate the DEFLATE body with no header. This may be useful in some situations.

C# program that uses DeflateStream using System.IO; using System.IO.Compression; class Program { static void Main() { CompressWithDeflate("C:\\programs\\example.txt", "C:\\programs\\deflate-output"); } static void CompressWithDeflate(string inputPath, string outputPath) { // Read in input file. byte[] b = File.ReadAllBytes(inputPath); // Write compressed data with DeflateStream. using (FileStream f2 = new FileStream(outputPath, FileMode.Create)) using (DeflateStream deflate = new DeflateStream(f2, CompressionMode.Compress, false)) { deflate.Write(b, 0, b.Length); } } }
A summary. We used GZipStream to compress to a file with an underlying FileStream. More complex methods are available for compression. This example alone does not meet most requirements.
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