Question

I am writing a basic Scanner class similar to Java’s. Here is what I have (well, the relevant parts):

using System.Text;
using System.Collections.Generic;

namespace System.IO
{
    /// <summary>
    ///     <remarks>
    ///         Scanner is a wrapper for a <see cref="System.IO.TextReader" />
    ///         instance, making it easier to read values of certain types. It
    ///         also takes advantage of the
    ///         <see cref="System.IO.EndOfStreamException" /> class.
    ///     </remarks>
    ///     <seealso cref="System.IO.TextReader" />
    /// </summary>
    public class Scanner
    {
        private TextReader Reader;
        private Queue<char> CharacterBuffer = new Queue<char>();

        /// <summary>
        ///     <remarks>
        ///         Defaults to reading from <see cref="Console.In"/>
        ///     </remarks>
        /// </summary>
        public Scanner() : this(Console.In)
        {
        }

        public Scanner(TextReader reader)
        {
            this.Reader = reader;
        }

        public char Peek()
        {
            if (this.CharacterBuffer.Count > 0)
                return this.CharacterBuffer.Peek();

            try
            {
                return Convert.ToChar(this.Reader.Peek());
            }
            catch (OverflowException)
            {
                throw new EndOfStreamException();
            }
        }

        public char ReadChar()
        {
            if (this.CharacterBuffer.Count > 0)
                return this.CharacterBuffer.Dequeue();

            try
            {
                return Convert.ToChar(this.Reader.Read());
            }
            catch (OverflowException)
            {
                throw new EndOfStreamException();
            }
        }
    }
}

From the few tests that I ran, this works great with real files, but it doesn’t quite work as expected with stdin. If I use Scanner.Peek or Scanner.ReadChar, after a newline is sent, the TextReader instance thinks it is at the end of the file (I think) and throws an EndOfStreamException instance since this.Reader.Read and this.Reader.Peek returns -1.

How can I force it to request a new character while still supporting true files and StringReader instances?

Answer 1

I changed Peek to reflect the following code. I’m not sure if this is 100% because I typed this from memory directly here.

public char Peek()
{
    if (this.CharacterBuffer.Count > 0)
        return this.CharacterBuffer.Peek();

    char Character
    try
    {
        Character = Convert.ToChar(this.Reader.Read());
    }
    catch (OverflowException)
    {
        throw new EndOfStreamException();
    }

    this.CharacterBuffer.Enqueue(Character);
    return Character;
}