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

Posted on 2008-06-13
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Last Modified: 2012-05-05
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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Question by:southparksystems
4 Comments
 
LVL 11

Accepted Solution

by:
dbrckovi earned 250 total points
ID: 21780458
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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Assisted Solution

by:Mike Tomlinson
Mike Tomlinson earned 250 total points
ID: 21780482
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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