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?
UPDATE
Back in my naïve 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.
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
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);
}
}
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);
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.
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();
}
}
}
}
}
}
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<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");
}
Hopefully this is helpful.
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);
}
}
}
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
Here is another open source library to create CSV file easily, Cinchoo ETL
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);
}
For more information, please read the CodeProject article on usage.
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);
}
}
enter code here
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();
You might just have to add a line feed "\n\r".
So I have this code:
class Program
{
static void Main(string[] args)
{
// Set a variable to the My Documents path.
string mydocpath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
var dir = new DirectoryInfo(mydocpath + #"\sample\");
string msg = "Created by: Johny";
foreach (var file in dir.EnumerateFiles("*.txt"))
{
file.AppendText(msg); //getting error here
}
}
}
And I want to add a footer to all the text file in the sample folder, but I'm getting an error because the AppendText is not accepting a string argument. I was just wondering how do I do this?
You want to use the streamwriter from AppendText I think:
static void Main(string[] args)
{
// Set a variable to the My Documents path.
string mydocpath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
var dir = new DirectoryInfo(mydocpath + #"\sample\");
string msg = "Created by: Johny";
foreach (var file in dir.EnumerateFiles("*.txt"))
{
var streamWriter = file.AppendText();
streamWriter.Write(msg);
streamWriter.Close();
}
}
FileInfo.AppendText() creates a StreamWriter, it doesn't append text per se. You want to do this:
using (var sw = file.AppendText()) {
sw.Write(msg);
}
AppendText is the extension method for the StreamWriter, see the documentation
So you should write these code instead:
foreach (var file in dir.EnumerateFiles("*.txt"))
{
using (StreamWriter sw = File.AppendText(file.FullName))
{
sw.WriteLine(msg);
}
}
I'm writing text to files using StreamWriter using the following code:
path == #"Desktop\";
filepath1 = path + "1.txt";
StreamWriter _sw = new StreamWriter(filepath1, true);
_sw.WriteLine("some Text");
_sw.Close();
if size of textfile exceeds 500kb I want to create text files dynamically. I'm tryng following code:
var size = (path.Length)/1024;
if(size>=500)
{
int i = (size/500)+1;
var filepath2 = path + i + ".txt";
if (File.Exists(filepath2))
{
StreamWriter _sw = new StreamWriter(filepath2, true);
_sw.WriteLine("Some message");
_sw.Close();
}
}
else
{
FileStream fs = File.Create(filepath2);
StreamWriter _sw = new StreamWriter(filepath2, true);
_sw.WriteLine(ex);
_sw.Close();
}
My question is if file 2.txt also exceeds 500kb I want to create 3.txt,4.txt..... and so on..
I want to create all these dynamically - how to solve this problem?
First thing you need to do the SIZE comparison for the data length of File not the File Path.
Here is Function which dose what you want to achieve, Please make appropriate changes for your path.
//Public variable to manage file names
int FileCounter = 1;
string FileName;
// Call this function to Add text to file
private void WriteToFile(string writeText)
{
FileName = "MyFile_"+FileCounter +".txt";
if (File.Exists(FileName))
{
string str = File.ReadAllText(FileName);
if ((str.Length + writeText.Length) / 1024 > 500) // check for limit
{
// Create new File
FileCounter++;
FileName = "MyFile_" + FileCounter + ".txt";
StreamWriter _sw = new StreamWriter(FileName, true);
_sw.WriteLine(writeText);
_sw.Close();
}
else // use exixting file
{
StreamWriter _sw = new StreamWriter(FileName, true);
_sw.WriteLine(writeText);
_sw.Close();
}
}
}
Where to start..
You are writing it as one big long procedural script. You need to break it down into chunks that can be reused using functions. As it is, it will get out of control way too quickly.
path == #"Desktop\"; is not valid. 1 too many =
Use Path.Combine() to combine your folder and filenames.
I'm sure this is all just test/rough/scratch code but just in case it's not, also check out Try/Except to wrap your file handling. You should also look up using() to dispose of your streams/writers.
My last comment would be that I see a lot of this sort of code a lot and it's often replaceable with something like Nlog for a whole lot less friction.
I would have commented but this login has no rep.