System.IO.StreamReader extension methods.

StreamReaderExtensions.cs

using System;
using System.IO;

namespace ExtensionMethods
{
    /// <summary>
    /// <see cref="StreamReader"/> extension methods.
    /// </summary>
    public static class StreamReaderExtensions
    {
        /// <summary>
        /// Gets the number of lines of the stream.
        /// </summary>
        /// <param name="reader">The <see cref="StreamReader"/>.</param>
        /// <returns>The number of lines of the stream.</returns>
        public static int CountLines(this StreamReader reader)
        {
            if (reader == null)
            {
                throw new ArgumentNullException(nameof(reader));
            }

            int count = 0;
            long previousPosition = reader.BaseStream.Position;
            reader.BaseStream.Position = 0;
            reader.DiscardBufferedData();

            while (reader.ReadLine() != null)
            {
                count++;
            }

            reader.BaseStream.Position = previousPosition;
            return count;
        }
    }
}