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".
I have a CSV file. I need to write a code that we can get a row from CSV by username. And I need to either update or delete that row from the CSV file. I was managed to get the row data by username. But I haven't got any idea how to write the code for Update or delete function. My code to get single row as follows
StreamReader reader = new StreamReader(System.IO.File.OpenRead(#"C:\Test\test.CSV"));
UserDetailsViewModel objInput = new UserDetailsViewModel();
while (!reader.EndOfStream)
{
string line = reader.ReadLine();
if (!String.IsNullOrWhiteSpace(line))
{
string[] values = line.Split(',');
if (values[0] == "Bharat")
{
objInput.FirstName = values[0];
objInput.LastName = values[1];
objInput.Address1 = values[2];
objInput.Address2 = values[3];
objInput.City = values[4];
objInput.State = values[5];
objInput.ZipCode = values[6];
break;
}
}
}
reader.Dispose();
return View(objInput);
Please someone help me to write a code for Update and delete on CSV file.
Thanks in Advance.
You can achieve your desired result, using below approach.
-> First you have to read your .csv file.
-> Then iterate through every line of file, meanwhile you can choose any row for edit/delete then make change to that row and store that row into string list.
-> At last you have to write string list to file. that's all.
For Example:
List<String> lines = new List<String>();
using (StreamReader reader = new StreamReader(System.IO.File.OpenRead(#"C:\Test\test.CSV"));)
{
String line;
while ((line = reader.ReadLine()) != null)
{
if (line.Contains(","))
{
String[] split = line.Split(',');
if (//condition for Edit record like : split[1] == "abc" etc.)
{
// update that
split[1] = "xyz";
line = String.Join(",", split);
lines.Add(line);
}
if (//condition for Delete row.)
{
// don't add that row into string list
}
}
}
}
using (StreamWriter writer = new StreamWriter(#"C:\Test\test.CSV", false))
{
foreach (String line in lines)
writer.WriteLine(line);
}
Reading and wirting csv is typically trickier than it seems to be at first glance.
Use a library like KBCsv (https://github.com/kentcb/KBCsv) for that task
How can I read line by line for a list of files?
I have a directory with a number of files, I need to save all the files in a list and process them one by one, line by line.
So far I have done the following :
//fetching all files from directory
DirectoryInfo d = new DirectoryInfo("path");
Dictionary<int, FileInfo> DatFiles = new Dictionary<int, FileInfo>();
int filecounter = 1;
foreach (var dat in d.EnumerateFiles())
{
DatFiles.Add(filecounter, dat);
filecounter++;
}
Console.WriteLine(filecounter);
foreach (var fileName in DatFiles)
{
foreach (var line in File.ReadLines(fileName.Value.OpenText().ToString()))
{
//run some methods
}
}
When executing, I'm getting an exception, file not found. Even though the list is full of file names.
EnumerateFiles() returns a list of FileInfo objects, and File.ReadLines() takes a string path argument; you probably want to use File.ReadLines(fileName.Value.FullName) in your foreach as that gives the path to the actual file; OpenText() returns a StreamReader object.
This smaller code should do the task
var files = Directory.GetFiles("path");
foreach(var f in files)
{
using(StreamReader reader = new StreamReader(f))
{
var lines = reader.ReadToEnd().Split(new string[]{Environment.NewLine});
// Do here
}
}
When all else fails refer to the documentation
// Open the stream and read it back.
using (StreamReader sr = fi.OpenText())
{
string s = "";
while ((s = sr.ReadLine()) != null)
{
Console.WriteLine(s);
}
}
I want to count the number of some strings and store it into a csv file. I've tried it but I don't know if this is the correct way and in addition, there are two problems.
First of all, here is my method:
public void CountMacNames(String macName)
{
string path = #"D:\Counter\macNameCounter.csv";
if (!File.Exists(path))
{
File.Create(path).Close();
}
var lines = File.ReadLines(path);
foreach (var line in lines)
{
bool isExists = line.Split(',').Any(x => x == macName);
if (isExists)
{
// macName exists, increment it's value by 1
}
else
{
// macName does not exists, add macName to CSV file and start counter by 1
var csv = new StringBuilder();
var newLine = string.Format("{0},{1}", macName, 1);
csv.AppendLine(newLine);
File.WriteAllText(path, csv.ToString());
}
}
}
The first problem is this IOException:
The process cannot access the file 'D:\Counter\macNameCounter.csv'
because it is being used by another process.
The second problem is, that I don't know how to increment the value by one, if a macName exists in the csv file (see first comment)
EDIT: Example for method "CountMacNames" call:
CountMacNames("Cansas");
CountMacNames("Wellback");
CountMacNames("Newton");
CountMacNames("Cansas");
CountMacNames("Princet");
Then, the CSV file should contain:
Cansas, 2
Wellback, 1
Newton, 1
Princet, 1
OK, this is what I'd do:
public void CountMacNames(String macName)
{
string path = #"D:\Counter\macNameCounter.csv";
// Read all lines, but only if file exists
string[] lines = new string[0];
if (File.Exists(path))
lines = File.ReadAllLines(path);
// This is the new CSV file
StringBuilder newLines = new StringBuilder();
bool macAdded = false;
foreach (var line in lines)
{
string[] parts = line.Split(',');
if (parts.Length == 2 && parts[0].Equals(macName))
{
int newCounter = Convert.ToIn32(parts[1])++;
newLines.AppendLine(String.Format("{0},{1}", macName, newCounter));
macAdded = true;
}
else
{
newLines.AppendLine(line.Trim());
}
}
if (!macAdded)
{
newLines.AppendLine(String.Format("{0},{1}", macName, 1));
}
File.WriteAllText(path, newLines.ToString());
}
This code does this:
Read all the lines from file only if it exists - otherwise we start a new file
Iterate over all the lines
If the first part of a 2-part line equals the mac, add 1 to counter and add line to output
If the first part doesn't match or the line format is wrong, add the line to output as is
If we didn't find the mac in any line, add a new line for the mac with counter 1
Write the file back
You can't read and write to the same file at the same time (in a simple way).
For small files, there are already answers.
If your file is really large (too big to fit in memory) you need another approach:
Read input file line by line
optinally modify the current line
write line to a temporary file
If finished delete input file, rename temporary file
For the first problem you can either read all the lines into memory and work there then write it all out again, or use streams.
using (FileStream fs = File.Open(filePath, FileMode.Create, FileAccess.ReadWrite))
{
var sw = new StreamWriter(fs);
var sr = new StreamReader(fs);
while(!streamReader.EndOfStream)
{
var line = sr.ReadLine();
//Do stuff with line.
//...
if (macExists)
{
//Increment the number, Note that in here we can only replace characters,
//We can't insert extra characters unless we rewrite the rest of the file
//Probably more hassle than it's worth but
//You could have a fixed number of characters like 000001 or 1
//Read the number as a string,
//Int.Parse to get the number
//Increment it
//work out the number of bytes in the line.
//get the stream position
//seek back to the beginning of the line
//Overwrite the whole line with the same number of bytes.
}
else
{
//Append a line, also harder to do with streams like this.
//Store the current position,
//Seek to the end of the file,
//WriteLine
//Seek back again.
}
}
}
You need to read the file in and release it, like this, to avoid the IO exception:
string[] lines = null;
using (var sr = new System.IO.StreamReader(path))
lines = sr.ReadToEnd().Split(new string[] {"\r", "\n"}, StringSplitOptions.RemoveEmptyEntries);
As for the count, you can just add an int value, change the method return type as int, too.
public int CountMacNames(String macName, String path)
{
if (!File.Exists(path))
{
File.Create(path).Close();
}
string[] lines = null;
using (var sr = new System.IO.StreamReader(path))
lines = sr.ReadToEnd().Split(new string[] {"\r", "\n"}, StringSplitOptions.RemoveEmptyEntries);
return lines.Where(p => p.Split(',').Contains(macName)).Count();
}
and inside the method that calls it:
var path = #"<PATH TO FILE>";
var cnt = CountMacNames("Canvas", path);
if (cnt > 0)
{
using (var sw = new StreamWriter(path, true, Encoding.Unicode))
sw.WriteLine(string.Format("Canvas,{0}", cnt));
}
Now, var res = CountMacNames("Canvas","PATH"); will return 2, and the lines "Canvas,2" or "Newton,1" will be appended to the file, without overwriting it.