C# – Reading a line from a streamreader without consuming


Is there a way to read ahead one line to test if the next line contains specific tag data?

I'm dealing with a format that has a start tag but no end tag.

I would like to read a line add it to a structure then test the line below to make sure it not a new "node" and if it isn't keep adding if it is close off that struct and make a new one

the only solution i can think of is to have two stream readers going at the same time kinda suffling there way along lock step but that seems wastefull (if it will even work)

i need something like peek but peekline

Best Solution

The problem is the underlying stream may not even be seekable. If you take a look at the stream reader implementation it uses a buffer so it can implement TextReader.Peek() even if the stream is not seekable.

You could write a simple adapter that reads the next line and buffers it internally, something like this:

 public class PeekableStreamReaderAdapter
        private StreamReader Underlying;
        private Queue<string> BufferedLines;

        public PeekableStreamReaderAdapter(StreamReader underlying)
            Underlying = underlying;
            BufferedLines = new Queue<string>();

        public string PeekLine()
            string line = Underlying.ReadLine();
            if (line == null)
                return null;
            return line;

        public string ReadLine()
            if (BufferedLines.Count > 0)
                return BufferedLines.Dequeue();
            return Underlying.ReadLine();