How to loop over each line from a TextReader?

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C# Reading a File Line By Line
How to loop over lines from a TextReader?

I am given a .NET TextReader (a class that can read a sequential series of characters). How can I loop over its content by line?

Note that given a `TextReader` you cannot be sure that you actually read "all" lines. If someone calls any of the `Read*()` methods before passing you the reference, you won't know. Whether that is an issue, YMMV. — Christian.K, Oct 02 '12 at 10:08
My answer would be the same as [last time you asked](http://stackoverflow.com/questions/12687453/how-to-loop-over-lines-from-a-textreader/12687525#12687525) — Rawling, Oct 02 '12 at 10:10
I wonder why it was so difficult to find it in the docs: [`TextReader.ReadLine` Method](http://msdn.microsoft.com/en-us/library/system.io.textreader.readline.aspx) — Tim Schmelter, Oct 02 '12 at 10:14

score 4 · Accepted Answer · answered Oct 02 '12 at 10:03

4

Do you mean something like this?

string line = null;
while((line = reader.ReadLine()) != null) 
{
    // do something with line
}

answered Oct 02 '12 at 10:03

Tudor

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Jon Skeet · Answer 2 · 2012-10-02T10:14:24.020

2

You can create an extension method very easily so that you can use foreach:

public static IEnumerable<string> ReadLines(this TextReader reader)
{
    string line = null;
    while((line = reader.ReadLine()) != null) 
    {
        yield return line;
    }
}

Note that this won't close the reader for you at the end.

You can then use:

foreach (string line in reader.ReadLines())

EDIT: As noted in comments, this is lazy. It will only read a line at a time, rather than reading all the lines into memory.

edited Oct 02 '12 at 10:14

answered Oct 02 '12 at 10:04

Jon Skeet

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Don't you mean `yield return line`? Is this... copied from another anwswer? 8-o – Rawling Oct 02 '12 at 10:12
@Rawling: Yes, I did mean that. And yes, I copied the boilerplaet bit :) – Jon Skeet Oct 02 '12 at 10:14
@ChibuezeOpata: Yes, this is lazy - now I've added the yield return properly! – Jon Skeet Oct 02 '12 at 10:14
1

I'm loving the duality of "lazy" here :p – Rawling Oct 02 '12 at 10:16
nice. though I think one of the readline's missing an s. – Chibueze Opata Oct 02 '12 at 18:38
@ChibuezeOpata: Where? The one *in the method* is meant to just read a single line. – Jon Skeet Oct 02 '12 at 18:38

Vishal Suthar · Answer 3 · 2012-10-02T10:09:44.923

You'd use it like this:

string line;
while ((line = myTextReader.ReadLine()) != null)
{
    //do whatever with "line";
}

OR

string Myfile = @"C:\MyDocument.txt";
using(FileStream fs = new FileStream(Myfile, FileMode.Open, FileAccess.Read))
{                    
    using(StreamReader sr = new StreamReader(fs))
    {
        while(!sr.EndOfStream)
        {
            Console.WriteLine(sr.ReadLine());
        }
    }
}

score 0 · Answer 4 · answered Oct 02 '12 at 10:05

0

The non-lazy solution I have at the moment:

foreach(string line in source.ReadToEnd().Split(Environment.NewLine.ToArray(),StringSplitOptions.None))

answered Oct 02 '12 at 10:05

Colonel Panic

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3

Why don't you put this in your original question? – Tudor Oct 02 '12 at 10:05

How to loop over each line from a TextReader?

4 Answers4