Random strings

In C# we generate random strings with a built-in method. This method, found in System.IO, generates random strings with high quality randomness. It is easy to use.

This problem can be approached in many ways, but the approaches that use the Random class have weaknesses. We can get repeating numbers due to the time-based seed value.

Example code

The Path.GetRandomFileName method is an effective way of generating strings. It uses RNGCryptoServiceProvider for better randomness, but is limited to 11 characters.

using System;
using System.IO;

/// <summary>
/// Random string generators.
/// </summary>
static class RandomUtil
{
    /// <summary>
    /// Get random string of 11 characters.
    /// </summary>
    /// <returns>Random string.</returns>
    public static string GetRandomString()
    {
        // Part 1: use GetRandomFileName.
        string path = Path.GetRandomFileName();

        // Part 2: remove period.
        path = path.Replace(".", "");
        return path;
    }
}

class Program
{
    static void Main()
    {
        // Part 3: test the random string method.
        Console.WriteLine(RandomUtil.GetRandomString());
        Console.WriteLine(RandomUtil.GetRandomString());
    }
}
wzp3t2j5a2o
ogj0xvz2pak

Cryptographic

GetRandomFileName uses RNGCryptoServiceProvider—this logic is cryptographic-strength. GetBytes is invoked internally and it returns random bytes.

With the Path class, we can obtain a random string. This method has a limitation on the length of the result, which means you may need to call it more than once or truncate the result.