Append data to a .csv File using C#

It looks to me like you want a new client to be added every time you click the button.

If that's the case, the reason why it doesn't work currently is that the file is being cleared by the line

File.WriteAllText(newFileName, clientHeader);

The simplest change would be to check if the file exists before writing over it:

if (!File.Exists(newFileName))
{
    //Header of the .csv File
    string clientHeader = "Client Name(ie. Billto_desc)" + "," + "Mid_id,billing number(ie billto_id)" + "," + "business unit id" + Environment.NewLine;

    File.WriteAllText(newFileName, clientHeader);
}

Although you could use other strategies, such as creating the file on startup of the application and keeping it open (using something like a StreamWriter). You would then close the writer when your application exited. This would pretty much guarantee that the file couldn't be messed with while your application is open.

You might want to do this because there is a race condition in that code - after you check the file exists, and before you write to the file, a user could delete it. Keeping the file open helps to avoid this, but you may or may not want to do it.

The underlying problem here seems to be where you're getting the data from to append to your CSV file. Your example code looks like it gets the various pieces of data from text boxes on the page, so if you want multiple clients, are they all going to have their data on the screen in text boxes? My instinct is probably not.

It sounds to me like you should be handling this client data using a class of some sort (perhaps persisted in a database) and then implement a method in the class called something like void AppendToCSV(string filename), which appends that client data to the CSV file. Then you can loop over your client objects, appending each one in turn.

How you produce/store your client objects, in relation to the text boxes you have on the screen, depends on what your app is trying to achieve.

I know this has been answered but there is what i did to create a "log" of subscribers. This uses reflection to get the properties and values of the object. Hope this helps someone in the future.

 internal static bool UpdateSubscriberList(MailingListEmail subscriber)
    {
        PropertyInfo[] propertyinfo;
        propertyinfo = typeof(MailingListEmail).GetProperties();
        var values = string.Empty;
        try
        {
            string fileName = @"C:\Development\test.csv";
            if (!File.Exists(fileName))
            {

                var header = string.Empty;
                foreach (var prop in propertyinfo)
                {
                    if (string.IsNullOrEmpty(header))
                        header += prop.Name;
                    else
                        header = string.Format("{0},{1}", header, prop.Name);


                }
                header = string.Format("{0},{1}", header, "CreatedDate");
                header += Environment.NewLine;
                File.WriteAllText(fileName, header);

            }


                foreach (var prop in propertyinfo)
                {
                    var value = prop.GetValue(subscriber, null);

                    if (string.IsNullOrEmpty(values))
                        values += value;
                    else
                        values = string.Format("{0},{1}", values, value);

                }
                values = string.Format("{0},{1}", values, DateTime.Now.ToShortDateString());

                values += Environment.NewLine;
                File.AppendAllText(fileName, values);



        }
        catch (Exception ex)
        {
            Elmah.ErrorSignal.FromCurrentContext().Raise(ex);
            return false;
        }


        return true;
    }

here is what i have done, and it works for me perfectly : first you need to creat DataTable from your listview, or just put data from textboxes:

 `public Boolean PreparCVS(string DateOne, string DataTwo)
    {
        try
        {
        // Create the `DataTable` structure according to your data source

            DataTable table = new DataTable();
            table.Columns.Add("HeaderOne", typeof(string));
            table.Columns.Add("HeaderTwo", typeof(String));

            // Iterate through data source object and fill the table
            table.Rows.Add(HeaderOne, HeaderTwo);
            //Creat CSV File
            CreateCSVFile(table, sCsvFilePath);
            return true;
        }
        catch (Exception ex)
        {
            throw new System.Exception(ex.Message);
        }
    }`

once dataTable is created you can generate CSV file by this method : in the streamwriter constructor you must specify in the second parameter True, by this, you can append data to you existing .csv file :

public void CreateCSVFile(DataTable dt, string strFilePath)
    {
        StreamWriter sw = new StreamWriter(strFilePath, true);

        int iColCount = dt.Columns.Count;
        for (int i = 0; i < iColCount; i++)
        {
            sw.Write(dt.Columns[i]);
            if (i < iColCount - 1)
            {
                sw.Write(",");
            }
        }
        sw.Write(sw.NewLine);

        foreach (DataRow dr in dt.Rows)
        {
            for (int i = 0; i < iColCount; i++)
            {
                if (!Convert.IsDBNull(dr[i]))
                {
                    sw.Write(dr[i].ToString());
                }
                if (i < iColCount - 1)
                {
                    sw.Write(",");
                }
            }
            sw.Write(sw.NewLine);
        }
        sw.Close();
    }

// At first read all the data from your first CSV

StreamReader oStreamReader = new StreamReader(@"d:\test\SourceFile.csv");
string recordsFromFirstFile = oStreamReader.ReadToEnd();
oStreamReader.Close();

// Now read the new records from your another csv file
oStreamReader = new StreamReader(@"d:\test\DestinationFile.csv");
string recordsFromSecondFile = oStreamReader.ReadToEnd();
oStreamReader.Close();
oStreamReader.Dispose();

// Here Records from second file will also contain column headers so we need to truncate them using Substring() method

recordsFromSecondFile = recordsFromSecondFile.Substring(recordsFromSecondFile.IndexOf('\n') + 1);

// Now merge the records either in SourceFile.csv or in Targetfile.csv or as per your required file

StreamWriter oStreamWriter= new StreamWriter(@"d:\testdata\TargetFile.csv");
oStreamWriter.Write(recordsFromFirstFile + recordsFromSecondFile);
oStreamWriter.Close();
oStreamWriter.Dispose();

Happy Coding.....

c#csv

using CsvHelper;

public void WriteDataToCsv(MsgEnvironmentData[] data, string csvPath) {

   if (!File.Exists(csvPath))
   {
     using (var writer = new StreamWriter(csvPath))
     using (var csvWriter = new CsvWriter(writer,firstConfiguration))
      {

          csvWriter.WriteHeader<MsgEnvironmentData>();
          csvWriter.NextRecord();
          csvWriter.WriteRecords(data);
      }
   }
   else
   {
       using (var stream = new FileStream(csvPath, FileMode.Append))
       using (var writer = new StreamWriter(stream))
       using (var csvWriter = new CsvWriter(writer, secondConfiguration))
        {
            csvWriter.WriteRecords(data);
        }
    }

}

Jeramy's answer writing the contents on last cell and from their horizontally in a row in csv file. I mixed and matched his solution with answer given here. I know this questions been asked long before but for the ones who doing research I'm posting the answer here.

string newFileName = @"C:\.NET\test.csv"; //filepath
var csv = new StringBuilder();
string clientDetails = "content1,content2,content3" + Environment.NewLine;
csv.Append(clientDetails);
File.AppendAllText(newFileName, csv.ToString());

I use this simple piece of code to append data to an existing CSV file:

        string[] data = { "John", "Doe", "25" };
        string csvFilePath = "example.csv";

        // Open the file for writing
        using (StreamWriter writer = File.AppendText(csvFilePath))
        {
            // Write the data row
            writer.WriteLine(string.Join(",", data));
        }