Writing data into CSV file in C

Question

I am trying to write into a csv file row by row using C  language  Here is my function  string first   reader 0  ToString    string second image ToString    string csv   string Format   0   1  n   first  second   File WriteAllText filePath  csv     The whole function runs inside a loop  and every row should be written to the csv file  In my case  next row overwrites the existing row and in the end  I am getting an only single record in the csv file which is the last one  How can I write all the rows in the csv file

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enter code here   string string value  string Empty           for  int i   0  i  lt  ur grid Rows Count  i                          for  int j   0  j  lt  ur grid Rows i  Cells Count  j                                  if   string IsNullOrEmpty ur grid Rows i  Cells j  Text ToString                                           if  j  gt  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

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public static class Extensions       public static void WriteCSVLine this StreamWriter writer  IEnumerable lt string gt  fields                const string q     quot  quot  quot  quot           writer WriteLine string Join  quot   quot               fields Select                  v   gt   v Contains         v Contains   quot       v Contains   n      v Contains   r        quot  q  v Replace q  q   q   q  quot    v                                 public static void WriteFields this StreamWriter writer  params string   fields    gt  WriteFields writer   IEnumerable lt string gt  fields      This should allow you to write a csv file quite simply  Usage  StreamWriter writer   new StreamWriter  quot myfile csv quot    writer WriteCSVLine new    quot A quot    quot B quot

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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   upd  Placed using in the right place

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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

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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

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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  lt  reader Count    i                  string first   reader i  ToString            string second   image ToString            string csvRow   string Format   0   1    first  second            stream WriteLine csvRow

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Here is another open source library to create CSV file easily  Cinchoo ETL  List lt dynamic gt  objs   new List lt dynamic gt      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       For more information  please read the CodeProject article on usage

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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  If you simply wanted to return the file instead of writing it to a location  this is an example of how I accomplished it   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 lt Person gt  list   new List lt Person gt         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        Hopefully this is helpful

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You might just have to add a line feed   n r

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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   gt         csv AppendLine string Join      line                     File WriteAllText filePath  csv ToString

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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

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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   quot C  mypath myfile csv quot          var writer   new CsvWriter textWriter  CultureInfo InvariantCulture       writer Configuration Delimiter    quot   quot        foreach  var item in list                writer WriteField   quot a quot             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 lt CsvRow gt  rows   new          new CsvRow  quot value1 quot   true       new CsvRow  quot value2 quot   false     using var textWriter   new StreamWriter   quot C  mypath myfile csv quot         var writer   new CsvWriter textWriter  CultureInfo InvariantCulture       writer Configuration Delimiter    quot   quot       writer WriteRecords rows       value1 true   value2 false   If you want to read more about the librarys configurations and possibilities you can do so here

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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

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UPDATE  Back in my na  ve days  I suggested doing this manually  it was a simple solution to a simple question   however due to this becoming more and more popular  I d recommend using the library CsvHelper that does all the safety checks  etc     CSV is way more complicated than what the question answer suggests   Original Answer  As you already have a loop  consider doing it 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       Or something to this effect  My reasoning is  you won t be need to write to the file for every item  you will only be opening the stream once and then writing to it   You can replace  File WriteAllText filePath  csv ToString       with   File AppendAllText filePath  csv ToString       if you want to keep previous versions of csv in the same file  C  6  If you are using c  6 0 then you can do the following  var newLine      first   second     EDIT  Here is a link to a question that explains what Environment NewLine does

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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  quot  0   1  2  quot   first  image  Environment NewLine

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