Question

I am creating a CSV file and I am using StringBuilder at the moment I come to a new Class “CommaDelimitedStringCollection“.

Can anyone tell me which is betterto use to write the file data. also what do you think of using TextWriter.

Thanks

Answer 1

If writing a CSV were a very complex task, I might rely on helpers like CommaDelimitedStringCollection. However, it isn’t complicated, so there’s no reason to introduce an extra helper class in here along with the associated perf hit.

If I needed to build a string in memory for some reason, such as implementing a general ToString() method, I would use StringBuilder instead of straight concatenation. However, in this case you are writing to a stream of some kind, so you don’t need this extra step either.

TextWriter is an abstract class, but you want the hierarchy of classes therein, specifically StreamWriter. This class has a number of constructor overloads; one takes a file name, if you want to write to a local file, and another takes a Stream object, if you want to write directly to a stream (for example Response.OutputStream in ASP.NET).

I actually did a quick Google search and there don’t appear to be any good examples of actually implementing a CSV download, if that’s what you’re trying to do, so here is one:

void ExportCsvAttachment(IEnumerable<Customer> customers)
{
    Response.Clear();
    Response.ContentType = "text/plain";
    Response.AddHeader("Content-Disposition: attachment;filename=Customers.csv");
    using (StreamWriter writer = new StreamWriter(Response.OutputStream))
    {
        WriteCsv(writer, customers);
    }
    Response.End();
}

void WriteCsv(TextWriter writer, IEnumerable<Customer> customers)
{
    foreach (Customer cust in customers)
    {
        writer.Write(cust.ID);
        writer.Write(',');
        WriteCsvString(writer, cust.Name);
        writer.Write(',');
        WriteCsvString(writer, cust.PhoneNumber);
    }
}

void WriteCsvString(TextWriter writer, string s)
{
    writer.Write('"');
    writer.Write(s.Replace("\"", "\"\""));
    writer.Write('"');
}

This uses the most common escaping mechanism for CSV – quotes around strings, another quote as an escape character.

If you just want to export to a local file instead, get rid of all the Response lines in ExportCsvAttachment and use the StreamWriter constructor that takes a path.