Creating a Random File in C#

Question

Well, a very simple solution:

byte[] data = new byte[sizeInMb * 1024 * 1024];
Random rng = new Random();
rng.NextBytes(data);
File.WriteAllBytes(fileName, data);

A slightly more memory efficient version 🙂

// Note: block size must be a factor of 1MB to avoid rounding errors :)
const int blockSize = 1024 * 8;
const int blocksPerMb = (1024 * 1024) / blockSize;
byte[] data = new byte[blockSize];
Random rng = new Random();
using (FileStream stream = File.OpenWrite(fileName))
{
    // There 
    for (int i = 0; i < sizeInMb * blocksPerMb; i++)
    {
        rng.NextBytes(data);
        stream.Write(data, 0, data.Length);
    }
}

However, if you do this several times in very quick succession creating a new instance of Random each time, you may get duplicate data. See my article on randomness for more information – you could avoid this using System.Security.Cryptography.RandomNumberGenerator… or by reusing the same instance of Random multiple times – with the caveat that it’s not thread-safe.

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