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copied!<p>If writing a CSV were a very complex task, I might rely on helpers like <code>CommaDelimitedStringCollection</code>. However, it isn't complicated, so there's no reason to introduce an extra helper class in here along with the associated perf hit.</p> <p>If I needed to build a string in memory for some reason, such as implementing a general <code>ToString()</code> method, I would use <code>StringBuilder</code> 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.</p> <p><code>TextWriter</code> is an abstract class, but you want the hierarchy of classes therein, specifically <code>StreamWriter</code>. 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 <code>Stream</code> object, if you want to write directly to a stream (for example <code>Response.OutputStream</code> in ASP.NET).</p> <p>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:</p> <pre><code>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('"'); } </code></pre> <p>This uses the most common escaping mechanism for CSV - quotes around strings, another quote as an escape character.</p> <p>If you just want to export to a local file instead, get rid of all the <code>Response</code> lines in <code>ExportCsvAttachment</code> and use the <code>StreamWriter</code> constructor that takes a path.</p>

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