Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace CSQuick
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var ff = new MemoryStream())
            using (var f = new StreamWriter(ff))
            {
                f.WriteLine("Stream hello world fail");
                f.Flush();
                using (TextReader ts = new StreamReader(ff))
                {
                    Console.WriteLine(ts.ReadToEnd());
                }
            }
        }
    }
}

Answer 1

Set
ff.Position = 0;
before reading, otherwise you start reading at the end of the stream.