[C#] Compressing a Directory to a ZIP File (ZipFile.CreateFromDirectory)

To combine the contents of a specific directory into a single ZIP file (archive), it is standard to use the CreateFromDirectory method of the System.IO.Compression.ZipFile class. Using this method allows you to complete the compression process with a single line of code, without having to write complex stream operations.

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Implementation Sample: Backing Up a Documents Folder

In the following code, we create dummy files inside a specified folder (MyDocuments) and then compress the entire folder into a file named MyDocuments_Backup.zip.

Sample Code

Note: In environments like .NET Framework, you may need to add a reference to System.IO.Compression.FileSystem.

using System;
using System.IO;
using System.IO.Compression; // Required for ZIP operations

public class Program
{
    public static void Main()
    {
        // The folder to compress (source)
        string sourceDir = "MyDocuments";
        
        // The path for the created ZIP file (destination)
        string zipPath = "MyDocuments_Backup.zip";

        // 1. Prepare the test environment
        // Create the folder and files beforehand
        if (Directory.Exists(sourceDir)) Directory.Delete(sourceDir, recursive: true);
        if (File.Exists(zipPath)) File.Delete(zipPath);

        Directory.CreateDirectory(sourceDir);
        File.WriteAllText(Path.Combine(sourceDir, "memo.txt"), "This is a meeting memo.");
        File.WriteAllText(Path.Combine(sourceDir, "budget.csv"), "100,200,300");

        try
        {
            Console.WriteLine($"Compressing folder '{sourceDir}'...");

            // 2. Compress the folder to a ZIP file
            // ZipFile.CreateFromDirectory(source directory, destination file path)
            ZipFile.CreateFromDirectory(sourceDir, zipPath);

            Console.WriteLine($"Compression complete: {Path.GetFullPath(zipPath)}");
        }
        catch (IOException ex)
        {
            // Occurs if a ZIP file with the same name already exists at the destination
            Console.WriteLine($"Error: {ex.Message}");
        }
    }
}

Execution Result

Compressing folder 'MyDocuments'...
Compression complete: C:\Work\MyDocuments_Backup.zip

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Explanation and Notes

1. Required Namespace

To use this feature, you must include using System.IO.Compression; at the top of your code.

2. Handling Duplicate Output Files

CreateFromDirectory throws an IOException if the destination ZIP file already exists. Since there is no built-in overwrite function, you should check for the file’s existence using File.Exists and delete it beforehand, or include a timestamp in the filename to ensure it is unique.

3. Character Encoding

In modern .NET (.NET Core / .NET 5 and later), UTF-8 encoding is used by default. This prevents character corruption even if Japanese filenames are included. If you need to force Shift-JIS for compatibility with standard Windows Explorer features in older environments, you must use an overloaded method that accepts a third argument for encoding.