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?
当前回答
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());
其他回答
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());
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。
你可能只需要添加换行符“\n\r”。
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();
}
}
}
}
}
}
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
