Question

Using a StreamReader, if you dispose the underlying stream, I thought you shouldn’t be able to read anymore.

That this is true suggests this question, where it’s suggested that you don’t have to dispose the StreamWriter (in their case) if the life of the underlying stream is handled elsewhere.

But that’s not the case. What I did was the following:

I have a file called delme.txt containing the following

abc
def
ghi

The I run this:

    Stream s = File.OpenRead(@"C:\delme.txt");
    StreamReader sr = new StreamReader(s, Encoding.ASCII);

    Console.WriteLine(sr.ReadLine());

    s.Dispose();

    Console.WriteLine(sr.ReadLine());

And the result is:

abc
def

How is this possible?

Answer 1

Your StreamReader already read the next line into its buffer.
It won’t go back to the source Stream until it runs out of data in its buffer.

In fact, it would be impossible for it to throw an exception in that case, since there is no idempotent way to find out whether a Stream has been disposed. (There is no IsDisposed property)