Question

我正在尝试使用C＃语言逐行写入csv文件。这是我的功能

string first = reader[0].ToString();
string second=image.ToString();
string csv = string.Format("{0},{1}\n", first, second);
File.WriteAllText(filePath, csv);

整个函数在循环内运行，每一行都应该写入csv文件。在我的情况下，下一行将覆盖现有行，最后，我在csv文件中获得了唯一一条记录，这是最后一行。如何编写csv文件中的所有行？

Answer 1

<强>更新

回到我天真的日子，我建议手动执行此操作（这是一个简单的问题的简单解决方案），但是由于这变得越来越流行，我建议使用库CsvHelper所有安全检查等。

CSV比问题/答案所暗示的要复杂得多。

原始答案

因为你已经有了一个循环，所以考虑这样做：

//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());

或者这种效果。我的理由是：你不需要为每个项目写入文件，你只会打开一次流然后写入它。

您可以替换

File.WriteAllText(filePath, csv.ToString());

带

File.AppendAllText(filePath, csv.ToString());

如果您想将以前版本的csv保留在同一个文件中

C＃6

如果您使用的是c＃6.0，则可以执行以下操作

var newLine = $"{first},{second}"

修改

以下是解释Environment.NewLine做什么
的问题link

Answer 2

我强烈建议你走更繁琐的路线。特别是如果你的文件很大。

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()打开一个新文件，写入内容然后关闭文件。打开文件是一项耗费大量资源的操作，而不是将数据写入开放流。打开\关闭循环内的文件将导致性能下降。

Johan建议的方法通过将所有输出存储在内存中然后将其写入一次来解决该问题。但是（如果是大文件），您的程序将消耗大量RAM，甚至会因OutOfMemoryException而崩溃

我的解决方案的另一个优点是您可以通过保存输入数据中的当前位置来实现暂停\恢复。

UPD。在正确的地方使用

Answer 3

手动编写csv文件可能很困难，因为您的数据可能包含逗号和换行符。我建议您使用现有的库。

这个问题提到了一些选择。

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

Answer 4

我使用两个解析解决方案，因为它很容易维护

// 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());

Answer 5

只需使用AppendAllText：

File.AppendAllText(filePath, csv);

~~AppendAllText的唯一缺点是当文件不存在时会抛出错误，所以必须检查~~

对不起，在阅读documentation之前的金发时刻。无论如何，如果文件存在，WriteAllText方法将覆盖先前在文件中写入的任何内容。

请注意，您当前的代码未使用正确的新行，例如在记事本中，您将全部视为一条长行。将代码更改为具有适当的新行：

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

Answer 6

您不应每次都调用AppendAllText()，而应考虑打开文件一次，然后再写一次整个内容：

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);
    }
}

Answer 7

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();
                    }
                }
            }
        }
    }
}

Answer 8

可以使用库而不是重新发明轮子。 CsvHelper非常适合创建和阅读csv文件。它的读写操作是基于流的，因此也支持大量数据的操作。

您可以像以下一样编写csv。

using(var textWriter = new StreamWriter(@"C:\mypath\myfile.csv"))
{
    var writer = new CsvWriter(textWriter);
    writer.Configuration.Delimiter = ",";

    foreach (var item in list)
    {
        writer.WriteField( "a" );
        writer.WriteField( 2 );
        writer.WriteField( true );
        writer.NextRecord();
    }
}

由于库正在使用反射，它将采用任何类型并直接解析它。

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);
    writer.Configuration.Delimiter = ",";
    writer.WriteRecords(rows);
}

值1，真

值2，假

如果您想了解更多关于图书馆配置和可能性的信息，请{... 3}}。

Answer 9

处理逗号

在使用string.Format(...)时，为了处理值内的逗号，以下内容对我有用：

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

所以要将它与Johan的答案结合起来，它看起来像这样：

//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());

返回CSV文件

如果您只是想返回文件而不是将其写入某个位置，这就是我如何完成它的一个示例：

来自存储过程

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");
}

从列表中

/* 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");
}

希望这很有帮助。

Answer 10

这是一个使用C＃创建csv文件的简单教程，您可以根据自己的需要进行编辑和扩展。

首先，您需要创建一个新的Visual Studio C＃控制台应用程序，有以下步骤可以执行此操作。

示例代码将在您指定的位置创建名为MyTest.csv的csv文件。该文件的内容应为3个命名列，前3行包含文本。

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);
        }
    }
}

Answer 11

您可能只需要添加换行符"\n\r"。

Answer 12

这是另一个可以轻松创建CSV文件的开源库，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);
}

有关详细信息，请阅读CodeProject有关使用情况的文章。

Answer 13

摆脱覆盖问题的一种简单方法是使用File.AppendText在文件末尾添加行

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);
    }
}

Answer 14

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();

Answer 15

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 WriteFields(this StreamWriter writer, params string[] fields) => WriteFields(writer, (IEnumerable<string>)fields);
}

这应该使您可以非常简单地编写一个csv文件。用法：

StreamWriter writer = new StreamWriter("myfile.csv");
writer.WriteCSVLine(new[]{"A", "B"});

在C＃中将数据写入CSV文件

15 个答案:

处理逗号

返回CSV文件

来自存储过程

从列表中