我试图用c#语言一行一行地写入csv文件。这是我的函数
string first = reader[0].ToString();
string second=image.ToString();
string csv = string.Format("{0},{1}\n", first, second);
File.WriteAllText(filePath, csv);
整个函数在循环中运行，每一行都应该写入csv文件。在我的例子中，下一行覆盖了现有的行，最后，我在csv文件中只得到一条记录，这是最后一条记录。如何写入csv文件中的所有行?
你可以使用AppendAllText代替:
File.AppendAllText(filePath, csv);
正如WriteAllText的文档所说:
如果目标文件已经存在，那么它将被覆盖
此外，请注意您当前的代码没有使用适当的新行，例如在记事本中，您将看到它都是一个长行。将代码更改为这样，以获得正确的新行:
string csv = string.Format("{0},{1}{2}", first, image, Environment.NewLine);
更新
回到我的naïve时代，我建议手动做这件事(这是一个简单问题的简单解决方案)，然而由于这变得越来越流行，我建议使用库CsvHelper来做所有的安全检查，等等。
CSV比问题/答案所暗示的要复杂得多。
原来的答案
因为你已经有了一个循环，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());
或者类似的东西。 我的理由是:你不需要为每一项写入文件，你只需要打开流一次，然后写入它。
你可以替换
File.WriteAllText(filePath, csv.ToString());
与
File.AppendAllText(filePath, csv.ToString());
如果您希望将CSV的以前版本保存在同一文件中
C# 6
如果您正在使用c# 6.0，那么您可以执行以下操作
var newLine = $"{first},{second}"
EDIT
这里有一个问题的链接，解释了什么环境。换行符。
我强烈建议你走更乏味的路线。尤其是当你的文件很大的时候。
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。与将数据写入开放流相比，打开文件是一个耗费大量资源的操作。在循环中打开/关闭文件会导致性能下降。
Johan建议的方法解决了这个问题，方法是将所有输出存储在内存中，然后只写入一次。然而(在大文件的情况下)，您的程序将消耗大量的RAM，甚至崩溃与OutOfMemoryException
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。
乌利希期刊指南。把使用放在正确的地方
而不是每次调用AppendAllText()，你可以考虑打开文件一次，然后写整个内容一次:
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);
}
}
我使用双解析解决方案，因为它非常容易维护
// 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());
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();
}
}
}
}
}
}
处理逗号
对于在使用string.Format(…)时处理值中的逗号，以下方法对我有用:
var newLine = string.Format("\"{0}\",\"{1}\",\"{2}\"",
first,
second,
third
);
csv.AppendLine(newLine);
所以把它和约翰的答案结合起来，看起来是这样的:
//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
如果你只是想返回文件，而不是把它写到一个位置，这是我如何完成它的一个例子:
从存储过程
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");
}
希望这对你们有帮助。
可以使用库而不是重新发明轮子。CsvHelper非常适合创建和读取csv文件。它的读写操作是基于流的，因此也支持有大量数据的操作。
您可以像下面这样编写csv文件。
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();
}
}
由于库正在使用反射，它将接受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, CultureInfo.InvariantCulture);
writer.Configuration.Delimiter = ",";
writer.WriteRecords(rows);
}
value1,真切
value2,假
如果你想阅读更多关于库的配置和可能性，你可以在这里这样做。
下面是另一个开源库，可以轻松创建CSV文件，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);
}
有关更多信息，请阅读CodeProject关于使用的文章。
这是一个使用c#创建csv文件的简单教程，您将能够编辑和扩展以适应自己的需要。
首先，您需要创建一个新的Visual Studio c#控制台应用程序，需要遵循以下步骤来完成此操作。
示例代码将在您指定的位置创建一个名为MyTest.csv的csv文件。文件的内容应该是3个命名列，前3行是文本。
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);
}
}
}
消除覆盖问题的一个简单方法是使用File。将行追加到文件的末尾作为
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();
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);
}
这将允许您非常简单地编写csv文件。用法:
StreamWriter writer = new ("myfile.csv");
writer.WriteCSVLine("A", "B"); // A,B
