How do you select the specific line to read in vb.net?

Question

I was wondering if/how you can read a specific line in vb.net using a system.io.streamreader.

Dim streamreader as system.io.streamreader
streamreader.selectline(linenumber as int).read
streamreader.close()

Is this possible or is there a similiar function to this one?

Answer 1

I'd use File.ReadAllLines to read in the lines into an array, then just use the array to select the line.

Dim allLines As String() = File.ReadAllLines(filePath)
Dim lineTwo As String = allLines(1) '0-based index

Note that ReadAllLines will read the entire text file into memory but I assume this isn't a problem because, if it is, then I suggest you take an alternative approach to trying to jump to a specific line.

Answer 2

ReadLines is pretty fast as it doesn't load everything in memory. It returns an IEnumerable<string> which allow you to skip to a line easily. Take this 5GB file:

var data = new string('A', 1022);
using (var writer = new StreamWriter(@"d:\text.txt"))
{
    for (int i = 1; i <= 1024 * 1024 * 5; i++)
    {
        writer.WriteLine("{0} {1}", i, data);
    }
}

var watch = Stopwatch.StartNew();
var line = File.ReadLines(@"d:\text.txt").Skip(704320).Take(1).FirstOrDefault();
watch.Stop();

Console.WriteLine("Elapsed time: {0}", watch.Elapsed); // Elapsed time: 00:00:02.0507396
Console.WriteLine(line); // 704320 AAAAAA...
Console.ReadLine();