Create a .csv file in C#

Question

Alright I want to create a .csv file in C#. I have been looking around and noticed a lot of people are using the system.IO.memorystream and system.io.streamwriter.

The problem is this: I have a web application. I want to give the user the ability to export to excel. Problem is, Excel cannot be installed on the server (don't ask). I want to be able to write an .csv sheet export for a report. Now, the reports headers and data will be different for all of the reports (looping through will solve this). Anybody have an example or better resources for me to go through?

Answer 1

This the approach i normally take. Probably not the most efficient though.

        /// <summary>
    /// Generates the contents of the log file.
    /// </summary>
    /// <returns>The contents of the log file.</returns>
    internal string GenerateLogFile()
    {
        StringBuilder csvExport = new StringBuilder();
        csvExport.AppendLine(Resources.CSVHeader);

        foreach (DataRow row in this.logEntries.Rows)
        {
            csvExport.AppendLine(
                string.Format(
                "\"{0}\",\"{1}\",\"{2}\",\"{3}\",\"{4}\",\"{5}\",\"{6}\",\"{7}\",\"{8}\", \"{9}\"",
                row[ColumnNames.LogTime], row[ColumnNames.Field1], row[ColumnNames.Field2], row[ColumnNames.Field3], row[ColumnNames.Field4], row[ColumnNames.Field5], row[ColumnNames.Field6], row[ColumnNames.Field7], row[ColumnNames.Field8], row[ColumnNames.Field9]));
        }

        return csvExport.ToString();
    }

    /// <summary>
    /// Adds the CSV file to the response.
    /// </summary>
    /// <param name="csvExportContents">The contents of the CSV file.</param>
    internal void DisplayLogFile(string csvExportContents)
    {
        byte[] data = new ASCIIEncoding().GetBytes(csvExportContents);

        HttpContext.Current.Response.Clear();
        HttpContext.Current.Response.ContentType = "APPLICATION/OCTET-STREAM";
        HttpContext.Current.Response.AppendHeader("Content-Disposition", "attachment; filename=Export.csv");
        HttpContext.Current.Response.OutputStream.Write(data, 0, data.Length);
        HttpContext.Current.Response.End();
    }

Answer 2

private void WriteItem<T>(StreamWriter sr, T item)
{
    string itemString = item.ToString();
    if(itemString.IndexOfAny(new char[] { '"', ',', '\n', '\r' }) != -1)//skip test and always escape for different speed/filesize optimisation
    {
        sr.Write('"');
        sr.Write(itemString.Replace("\"", "\"\""));
        sr.Write('"');
    }
    else
        sr.Write(itemString);
}
private void WriteLine<T>(StreamWriter sr, IEnumerable<T> line)
{
    bool first = true;
    foreach(T item in line)
    {
        if(!first)
            sr.Write(',');
        first = false;
        WriteItem(sr, item);
    }
}
private void WriteCSV<T>(StreamWriter sr, IEnumerable<IEnumerable<T>> allLines)
{
    bool first = true;
    foreach(IEnumerable<T> line in allLines)
    {
        if(!first)
            sr.Write('\n');
        first = false;
        WriteLine(sr, line);
    }
}
private void WriteCSV<T>(HttpResponse response, IEnumerable<IEnumerable<T>> allLines)
{
    response.ContentType = "text/csv";
    WriteCSV(response.Output, allLines);
}

It can be worth also sending a content-disposition header with a recommended filename.

Edit: Of late, with cases where one needs to interspace an action between items in an enumeration (like the comma and newline above), I've preferred that rather keeping a boolean that keeps being checked, I handle the enumerator directly, and then handle the first element separate from the rest. I started doing this as a micro-opt in a efficiency-push but have grown to just find it a better expression of a code-path that differs for the first item. As such, I'd now write the above as:

private void WriteLine<T>(StreamWriter sr, IEnumerable<T> line)
{
  using(var en = line.GetEnumerator())
  if(en.MoveNext())
  {
    WriteItem(sr, en.Current);
    while(en.MoveNext())
    {
      sr.Write(',');
      WriteItem(sr, en.Current);
    }
}
private void WriteCSV<T>(StreamWriter sr, IEnumerable<IEnumerable<T>> allLines)
{
    using(var en = allLines.GetEnumerator())
    if(en.MoveNext())
    {
      WriteLine(sr, en.Current);
      while(en.MoveNext())
      {
        sr.Write('\n');
        WriteLine(sr, en.Current);
      }
    }
}