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

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();
                    }
                }
            }
        }
    }
}

其他回答

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();

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。

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);
    }
}
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();
                    }
                }
            }
        }
    }
}