StreamReader ReadLine is modifying / not releasing a Stream

Question

I am using FileHelpers to parse CSV files uploaded on an ASP.NET app.

Two different CSV file structures (ie. different amount of columns) will be uploaded, so before I create the FileHelpers engine with the model of the structure to be parsed, I read the first line of the file like this:

string line = "";

using (StreamReader reader = new StreamReader(file.InputStream))
{
    line = reader.ReadLine();
}

int fieldCount = line.Count(l => l == ',');

This works, and gives me the column count, but it breaks anything else I want to do with file.InputStream:

var engine = new FileHelperEngine<CSVModel>();
CSVModel[] records;
records = (CSVModel[])engine.ReadStream(new StreamReader(file.InputStream),
    Int32.MaxValue);
// etc etc

Why does this happen? I've tried to take away the using and just manually close() the StreamReader but it doesn't help.

score 1 · Accepted Answer · edited May 23 '17 at 12:11

1

The problem you're experiencing is because the built in Stream classes dispose the underlying stream once they themselves are disposed or closed.

As counter-intuitive as it is, you'll either need to not close the stream if you're still using it, re-open it before accessing it, or copy it into a MemorStream if you want to use it in more than one place.

This question has some explanations.

Edit: (After Jim's comment)

Alternatively you can inform the StreamReader not to close the underlying stream by using a parameter in the constructor. (MSDN Documentation)

edited May 23 '17 at 12:11

Community

1
1

answered Sep 18 '13 at 14:08

Matthew Steeples

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In .NET 4.5 there's a [constructor that lets you tell it to leave the underlying stream open](http://msdn.microsoft.com/en-us/library/gg712952.aspx). – Jim Mischel Sep 18 '13 at 16:08
Wow, thanks for that @JimMischel. I'll update my answer to include your comment. – Matthew Steeples Sep 18 '13 at 16:26

score 0 · Answer 2 · answered Sep 18 '13 at 13:43

0

You should reset the position of the stream after the first read:

file.InputStream.Position = 0;

answered Sep 18 '13 at 13:43

Alberto

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That will not work. `StreamReader` has an internal buffer. So if you reset the underlying stream's position, things will get all jumbled the next time the `StreamReader` goes to update its buffer. – Jim Mischel Sep 18 '13 at 16:10

StreamReader ReadLine is modifying / not releasing a Stream

2 Answers2