Writing data into CSV file in C#

I would highly recommend you to go the more tedious route. Especially if your file size is large.

using(var w = new StreamWriter(path)) { for( /* your loop */) { var first = yourFnToGetFirst(); var second = yourFnToGetSecond(); var line = string.Format("{0},{1}", first, second); w.WriteLine(line); w.Flush(); } } 

File.AppendAllText() opens a new file, writes the content and then closes the file. Opening files is a much resource-heavy operation, than writing data into open stream. Opening\closing a file inside a loop will cause performance drop.

The approach suggested by Johan solves that problem by storing all the output in memory and then writing it once. However (in case of big files) you program will consume a large amount of RAM and even crash with OutOfMemoryException

Another advantage of my solution is that you can implement pausing\resuming by saving current position in input data.

Writing csv files by hand can be difficult because your data might contain commas and newlines. I suggest you use an existing library instead.

This question mentions a few options.

Are there any CSV readers/writer libraries in C#?

I use a two parse solution as it's very easy to maintain

// Prepare the values var allLines = (from trade in proposedTrades select new object[] { trade.TradeType.ToString(), trade.AccountReference, trade.SecurityCodeType.ToString(), trade.SecurityCode, trade.ClientReference, trade.TradeCurrency, trade.AmountDenomination.ToString(), trade.Amount, trade.Units, trade.Percentage, trade.SettlementCurrency, trade.FOP, trade.ClientSettlementAccount, string.Format("\"{0}\"", trade.Notes), }).ToList(); // Build the file content var csv = new StringBuilder(); allLines.ForEach(line => { csv.AppendLine(string.Join(",", line)); }); File.WriteAllText(filePath, csv.ToString()); 

Instead of calling every time AppendAllText() you could think about opening the file once and then write the whole content once:

var file = @"C:\myOutput.csv"; using (var stream = File.CreateText(file)) { for (int i = 0; i < reader.Count(); i++) { string first = reader[i].ToString(); string second = image.ToString(); string csvRow = string.Format("{0},{1}", first, second); stream.WriteLine(csvRow); } } 

Instead of reinventing the wheel a library could be used. CsvHelper is great for creating and reading csv files. It's read and write operations are stream based and therefore also support operations with a big amount of data.

You can write your csv like the following.

using(var textWriter = new StreamWriter(@"C:\mypath\myfile.csv")) { var writer = new CsvWriter(textWriter, CultureInfo.InvariantCulture); writer.Configuration.Delimiter = ","; foreach (var item in list) { writer.WriteField( "a" ); writer.WriteField( 2 ); writer.WriteField( true ); writer.NextRecord(); } } 

As the library is using reflection it will take any type and parse it directly.

public class CsvRow { public string Column1 { get; set; } public bool Column2 { get; set; } public CsvRow(string column1, bool column2) { Column1 = column1; Column2 = column2; } } IEnumerable<CsvRow> rows = new [] { new CsvRow("value1", true), new CsvRow("value2", false) }; using(var textWriter = new StreamWriter(@"C:\mypath\myfile.csv") { var writer = new CsvWriter(textWriter, CultureInfo.InvariantCulture); writer.Configuration.Delimiter = ","; writer.WriteRecords(rows); } 

value1,true

value2,false

If you want to read more about the librarys configurations and possibilities you can do so here.

You can use AppendAllText instead:

File.AppendAllText(filePath, csv); 

As the documentation of WriteAllText says:

If the target file already exists, it is overwritten

Also, note that your current code is not using proper new lines, for example in Notepad you'll see it all as one long line. Change the code to this to have proper new lines:

string csv = string.Format("{0},{1}{2}", first, image, Environment.NewLine); 

using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using System.Data; using System.Configuration; using System.Data.SqlClient; public partial class CS : System.Web.UI.Page { protected void ExportCSV(object sender, EventArgs e) { string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString; using (SqlConnection con = new SqlConnection(constr)) { using (SqlCommand cmd = new SqlCommand("SELECT * FROM Customers")) { using (SqlDataAdapter sda = new SqlDataAdapter()) { cmd.Connection = con; sda.SelectCommand = cmd; using (DataTable dt = new DataTable()) { sda.Fill(dt); //Build the CSV file data as a Comma separated string. string csv = string.Empty; foreach (DataColumn column in dt.Columns) { //Add the Header row for CSV file. csv += column.ColumnName + ','; } //Add new line. csv += "\r\n"; foreach (DataRow row in dt.Rows) { foreach (DataColumn column in dt.Columns) { //Add the Data rows. csv += row[column.ColumnName].ToString().Replace(",", ";") + ','; } //Add new line. csv += "\r\n"; } //Download the CSV file. Response.Clear(); Response.Buffer = true; Response.AddHeader("content-disposition", "attachment;filename=SqlExport.csv"); Response.Charset = ""; Response.ContentType = "application/text"; Response.Output.Write(csv); Response.Flush(); Response.End(); } } } } } } 

This is a simple tutorial on creating csv files using C# that you will be able to edit and expand on to fit your own needs.

First you’ll need to create a new Visual Studio C# console application, there are steps to follow to do this.

The example code will create a csv file called MyTest.csv in the location you specify. The contents of the file should be 3 named columns with text in the first 3 rows.

https://tidbytez.com/2018/02/06/how-to-create-a-csv-file-with-c/

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; using System.IO; namespace CreateCsv { class Program { static void Main() { // Set the path and filename variable "path", filename being MyTest.csv in this example. // Change SomeGuy for your username. string path = @"C:\Users\SomeGuy\Desktop\MyTest.csv"; // Set the variable "delimiter" to ", ". string delimiter = ", "; // This text is added only once to the file. if (!File.Exists(path)) { // Create a file to write to. string createText = "Column 1 Name" + delimiter + "Column 2 Name" + delimiter + "Column 3 Name" + delimiter + Environment.NewLine; File.WriteAllText(path, createText); } // This text is always added, making the file longer over time // if it is not deleted. string appendText = "This is text for Column 1" + delimiter + "This is text for Column 2" + delimiter + "This is text for Column 3" + delimiter + Environment.NewLine; File.AppendAllText(path, appendText); // Open the file to read from. string readText = File.ReadAllText(path); Console.WriteLine(readText); } } } 

Handling Commas

For handling commas inside of values when using string.Format(...), the following has worked for me:

var newLine = string.Format("\"{0}\",\"{1}\",\"{2}\"", first, second, third ); csv.AppendLine(newLine); 

So to combine it with Johan's answer, it'd look like this:

//before your loop var csv = new StringBuilder(); //in your loop var first = reader[0].ToString(); var second = image.ToString(); //Suggestion made by KyleMit var newLine = string.Format("\"{0}\",\"{1}\"", first, second); csv.AppendLine(newLine); //after your loop File.WriteAllText(filePath, csv.ToString()); 

Returning CSV File

From a Stored Procedure

public FileContentResults DownloadCSV() { // I have a stored procedure that queries the information I need SqlConnection thisConnection = new SqlConnection("Data Source=sv12sql;User ID=UI_Readonly;Password=SuperSecure;Initial Catalog=DB_Name;Integrated Security=false"); SqlCommand queryCommand = new SqlCommand("spc_GetInfoINeed", thisConnection); queryCommand.CommandType = CommandType.StoredProcedure; StringBuilder sbRtn = new StringBuilder(); // If you want headers for your file var header = string.Format("\"{0}\",\"{1}\",\"{2}\"", "Name", "Address", "Phone Number" ); sbRtn.AppendLine(header); // Open Database Connection thisConnection.Open(); using (SqlDataReader rdr = queryCommand.ExecuteReader()) { while (rdr.Read()) { // rdr["COLUMN NAME"].ToString(); var queryResults = string.Format("\"{0}\",\"{1}\",\"{2}\"", rdr["Name"].ToString(), rdr["Address"}.ToString(), rdr["Phone Number"].ToString() ); sbRtn.AppendLine(queryResults); } } thisConnection.Close(); return File(new System.Text.UTF8Encoding().GetBytes(sbRtn.ToString()), "text/csv", "FileName.csv"); } 

From a List

/* To help illustrate */ public static List<Person> list = new List<Person>(); /* To help illustrate */ public class Person { public string name; public string address; public string phoneNumber; } /* The important part */ public FileContentResults DownloadCSV() { StringBuilder sbRtn = new StringBuilder(); // If you want headers for your file var header = string.Format("\"{0}\",\"{1}\",\"{2}\"", "Name", "Address", "Phone Number" ); sbRtn.AppendLine(header); foreach (var item in list) { var listResults = string.Format("\"{0}\",\"{1}\",\"{2}\"", item.name, item.address, item.phoneNumber ); sbRtn.AppendLine(listResults); } } return File(new System.Text.UTF8Encoding().GetBytes(sbRtn.ToString()), "text/csv", "FileName.csv"); } 

public static class Extensions { public static void WriteCSVLine(this StreamWriter writer, IEnumerable<string> fields) { const string q = @""""; writer.WriteLine(string.Join(",", fields.Select( v => (v.Contains(',') || v.Contains('"') || v.Contains('\n') || v.Contains('\r')) ? $"{q}{v.Replace(q, q + q)}{q}" : v ))); } public static void WriteCSVLine(this StreamWriter writer, params string[] fields) => WriteCSVLine(writer, (IEnumerable<string>)fields); } 

This should allow you to write a csv file quite simply. Usage:

StreamWriter writer = new ("myfile.csv"); writer.WriteCSVLine("A", "B"); // A,B 

(disclaimer: I'm about to recommend a project I'm involved in)

I've been maintaining an open-source CSV writer library since 2015: https://github.com/jitbit/CsvExport

It's Excel-compatible, escapes commas/quotes/multiline, exports dates in timezone-proof format, etc. It's .NET standard 2.0, works with .NET Core, and .NET Framework.

Usage:

var myExport = new CsvExport(); myExport.AddRow(); myExport["Region"] = "Denver, USA"; myExport["Sales"] = 100000; myExport["Date Opened"] = new DateTime(2003, 12, 31); myExport.AddRow(); myExport["Region"] = "London \"in\" the UK"; myExport["Sales"] = 50000; myExport["Date Opened"] = new DateTime(2005, 1, 1, 9, 30, 0); //ASP.NET MVC action example return File(myExport.ExportToBytes(), "text/csv", "results.csv"); 

Available on Nuget:

Install-Package CsvExport 

One simple way to get rid of the overwriting issue is to use File.AppendText to append line at the end of the file as

void Main() { using (System.IO.StreamWriter sw = System.IO.File.AppendText("file.txt")) { string first = reader[0].ToString(); string second=image.ToString(); string csv = string.Format("{0},{1}\n", first, second); sw.WriteLine(csv); } } 

Here is another open source library to create CSV file easily, Cinchoo ETL

METHOD 1: Dynamic Model

List<dynamic> objs = new List<dynamic>(); dynamic rec1 = new ExpandoObject(); rec1.Id = 10; rec1.Name = @"Mark"; rec1.JoinedDate = new DateTime(2001, 2, 2); rec1.IsActive = true; rec1.Salary = new ChoCurrency(100000); objs.Add(rec1); dynamic rec2 = new ExpandoObject(); rec2.Id = 200; rec2.Name = "Tom"; rec2.JoinedDate = new DateTime(1990, 10, 23); rec2.IsActive = false; rec2.Salary = new ChoCurrency(150000); objs.Add(rec2); using (var parser = new ChoCSVWriter("emp.csv").WithFirstLineHeader()) { parser.Write(objs); } 

METHOD 2: POCO Model

List<Emp> objs = new List<Emp>(); Emp rec1 = new Emp(); rec1.Id = 10; rec1.Name = @"Mark"; objs.Add(rec1); Emp rec2 = new Emp(); rec2.Id = 200; rec2.Name = "Tom"; objs.Add(rec2); using (var parser = new ChoCSVWriter<Emp>("emp.csv").WithFirstLineHeader()) { parser.Write(objs); } 

For more information, please read the CodeProject article on usage.

You might just have to add a line feed "\n\r".

 string string_value= string.Empty; for (int i = 0; i < ur_grid.Rows.Count; i++) { for (int j = 0; j < ur_grid.Rows[i].Cells.Count; j++) { if (!string.IsNullOrEmpty(ur_grid.Rows[i].Cells[j].Text.ToString())) { if (j > 0) string_value= string_value+ "," + ur_grid.Rows[i].Cells[j].Text.ToString(); else { if (string.IsNullOrEmpty(string_value)) string_value= ur_grid.Rows[i].Cells[j].Text.ToString(); else string_value= string_value+ Environment.NewLine + ur_grid.Rows[i].Cells[j].Text.ToString(); } } } } string where_to_save_file = @"d:\location\Files\sample.csv"; File.WriteAllText(where_to_save_file, string_value); string server_path = "/site/Files/sample.csv"; Response.ContentType = ContentType; Response.AppendHeader("Content-Disposition", "attachment; filename=" + Path.GetFileName(server_path)); Response.WriteFile(server_path); Response.End();