Let us have a look at my XLS to CSV Converter class today.

It is a static class, which is located in the Core.CSV namespace. It contains one static method CovertExcelToCsv which takes 3 parameters excelFilePath, csvOutputFile and worksheetNumber. The excelFilePath parameter is used to input the source Excel file, csvOutputFile is used to input the destination CSV file and lastly worksheetNumber is used to define which worksheet to convert, as CSV files do not have worksheets only one worksheet can be converted to CSV file at a time. The worksheetNumber parameter has a default value of 1 in the event that no value is passed in.

using System;
using System.Data;
using System.Data.OleDb;
using System.IO;

namespace Core.CSV
{
 public static class XlsToCsvConverter
 {
  public static void CovertExcelToCsv(string excelFilePath, string csvOutputFile, int worksheetNumber = 1)
  {
   if (!File.Exists(excelFilePath)) throw new FileNotFoundException(excelFilePath);
   if (File.Exists(csvOutputFile)) throw new ArgumentException("File exists: " + csvOutputFile);

   // Connection string
   var connectionStr =
    String.Format(
     "Provider=Microsoft.Jet.OLEDB.4.0;Data Source={0};Extended Properties=\"Excel 8.0;IMEX=1;HDR=NO\"",
     excelFilePath);
   var cnn = new OleDbConnection(connectionStr);

   // Get schema information and then data in spreadsheet
   var dt = new DataTable();
   try
   {
    cnn.Open();
    var schemaTable = cnn.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null);
    if (schemaTable != null && schemaTable.Rows.Count < worksheetNumber)
     throw new ArgumentException("The worksheet number requested does not exist.");
    if (schemaTable != null)
    {
     var worksheet = schemaTable.Rows[worksheetNumber - 1]["table_name"].ToString().Replace("'", "");
     var sql = String.Format("select * from [{0}]", worksheet);
     var da = new OleDbDataAdapter(sql, cnn);
     da.Fill(dt);
    }
   }
   catch (Exception ex)
   {
    //Insert logging of exception here
    throw;
   }
   finally
   {
    // Close connection to the spreadsheet
    cnn.Close();
   }

   // Write out CSV data
   using (var wtr = new StreamWriter(csvOutputFile))
   {
    foreach (DataRow row in dt.Rows)
    {
     var firstLine = true;
     foreach (DataColumn col in dt.Columns)
     {
      if (!firstLine)
      {
       wtr.Write(",");
      }
      else
      {
       firstLine = false;
      }
      var data = row[col.ColumnName].ToString().Replace("\"", "");
      wtr.Write(String.Format("{0}", data));
     }
     wtr.WriteLine();
    }
   }
  }
 }
}