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re reading the last line again with StreamReader.ReadLine()

In the example below I need to use sr.ReadLine() to read the lines out of a text file. Sometimes I may want to back the position of the streamreader up to the beginning of the previous line, so that the next call to sr.ReadLine() reads the previous line again. sr.BaseStream.Seek doesn't seem to be working for me and the sr.BaseStream.Position doesn't seem to reflect what I expect.
string filePath = @"c:\temp\debug.txt";
 
using (StreamReader sr = new StreamReader(filePath))
{
    string line1 = sr.ReadLine();
    string line2 = sr.ReadLine();
 
    // Back up so the next ReadLine reads line 2 again
    sr.BaseStream.Seek(-line2.Length, SeekOrigin.Current);
    sr.DiscardBufferedData();
 
    string line2Again = sr.ReadLine();
 
    if (line2 != line2Again)
    {
        Console.Write("This is not what I expect");
    }
}

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southparksystems
Asked:
southparksystems
2 Solutions
 
dbrckoviCommented:
Hi!

You could load the complete file in some kind of collection, and work with it.
Maybe something like this:


    public partial class Form1 : Form
    {
        StreamReader SR;
        List<string> FileLines = new List<string>();
 
        public Form1()
        {
            InitializeComponent();
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            MessageBox.Show("First line: " + FileLines[0]);
            MessageBox.Show("Last line: " + FileLines[FileLines.Count - 1]);
            MessageBox.Show("Line before last: " + FileLines[FileLines.Count - 2]);
        }
 
        private void Form1_Load(object sender, EventArgs e)
        {
            //load all lines
            SR = File.OpenText("c:\\aaa\\aaa.txt");
            string CurrentLine = "";
            do
            {
                CurrentLine = SR.ReadLine();
                if (CurrentLine != null && CurrentLine.Length != 0)
                {
                    FileLines.Add(CurrentLine);
                }
            } while (CurrentLine != null && CurrentLine.Length != 0);
 
            SR.Close();
            MessageBox.Show("Lines in file: " + FileLines.Count);
        }
    }

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Mike TomlinsonMiddle School Assistant TeacherCommented:
ReadLine() strips off the carriage return/line feed at the end of the line...so you need to compensate for that.
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