c# Csv文件读写示例，如果文件存在追加写入

功能

1.写入

2.读取

导出文件效果

调用示例

注意示例中的ToDataTable()方法是自己的封装的扩展方法，源码在集合扩展方法-CSDN博客

private List<MarkDataModel> createMarkDataList(int count)
        {
            var markDataModels = new List<MarkDataModel>();
            for (int i = 0; i < count; i++)
            {
                markDataModels.Add(new MarkDataModel()
                {
                    X = i + 1,
                    Y = i + 1,
                    Text = "Data" + i + "_" + DateTime.Now.ToString("HHmmssfff")
                });
            }
            return markDataModels;
        }

        /// <summary>
        /// 写入
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnWrite_Click(object sender, EventArgs e)
        {
            var dataList = createMarkDataList(10);
            //var filePath = AppContext.BaseDirectory + @"WeldResultUpload\" + DateTime.Now.ToString("yyyyMMdd") + @"\" + Global.GlobalIns.MaterialsCodeCurrent + ".xlsx";
            string currentDirectory = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
            currentDirectory += @"ResultUpload\" + DateTime.Now.ToString("yyyyMMdd") + ".csv";
            CsvHelper.SaveCSV(dataList.ToDataTable(), currentDirectory);

            var dataList2 = createMarkDataList(20);
            CsvHelper.SaveCSV(dataList2.ToDataTable(), currentDirectory);
            MessageBox.Show("导出完成");
        }

Csv文件帮助类

using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Text;
using System.IO;

namespace CSVWinFormsApp
{
    /// <summary>
    /// Csv文件帮助类
    /// </summary>
    public class CsvHelper
    {
        /// <summary>
        /// 写入CSV文件
        /// </summary>
        /// <param name="dt">要写入的数据表</param>
        /// <param name="fullPath">保存的文件路径，注意包含文件名</param>
        public static void SaveCSV(DataTable dt, string fullPath)
        {
            try
            {
                FileInfo fi = new FileInfo(fullPath);
                //判断文件目录是否存在
                if (!fi.Directory.Exists)
                {
                    //如果目录不存在就创建目录
                    fi.Directory.Create();
                }

                var isExists = File.Exists(fullPath);
                //FileMode.Append 如果文件存在追加写入
                using (FileStream fs = new FileStream(fullPath, FileMode.Append,
                        FileAccess.Write))
                {
                    StreamWriter sw = new StreamWriter(fs, System.Text.Encoding.UTF8);
                    string data = string.Empty;

                    if (!isExists)
                    {
                        for (int i = 0; i < dt.Columns.Count; i++)//写入列名
                        {
                            data += dt.Columns[i].ColumnName.ToString();
                            if (i < dt.Columns.Count - 1)
                            {
                                data += ",";
                            }
                        }
                        sw.WriteLine(data);
                    }

                    for (int i = 0; i < dt.Rows.Count; i++) //写入各行数据
                    {
                        data = string.Empty;
                        for (int j = 0; j < dt.Columns.Count; j++)
                        {
                            string str = dt.Rows[i][j].ToString();
                            str = str.Replace("\"", "\"\"");//替换英文冒号 英文冒号需要换成两个冒号
                            if (str.Contains(',') || str.Contains('"')
                              || str.Contains('\r') || str.Contains('\n')) //含逗号 冒号 换行符的需要放到引号中
                            {
                                str = string.Format("\"{0}\"", str);
                            }

                            data += str;
                            if (j < dt.Columns.Count - 1)
                            {
                                data += ",";
                            }
                        }
                        sw.WriteLine(data);
                    }
                    //使用了Using可以不手动关闭了。好买书还是关一下的好
                    sw.Close();
                    fs.Close();
                }
            }
            catch (Exception ex)
            {

            }
        }

        /// <summary>
        /// 打开CSV文件
        /// </summary>
        /// <param name="filePath"></param>
        /// <returns></returns>
        public static DataTable OpenCSV(string filePath)//从csv读取数据返回table
        {
            System.Text.Encoding encoding = GetType(filePath); //Encoding.ASCII;//
            DataTable dt = new DataTable();

            try
            {
                using (FileStream fs = new FileStream(filePath, FileMode.Open,
                            FileAccess.Read))
                {
                    StreamReader sr = new StreamReader(fs, encoding);

                    //记录每次读取的一行记录
                    string strLine = string.Empty;
                    //记录每行记录中的各字段内容
                    string[] aryLine = null;
                    string[] tableHead = null;
                    //标示列数
                    int columnCount = 0;
                    //标示是否是读取的第一行
                    bool IsFirst = true;
                    //逐行读取CSV中的数据
                    while ((strLine = sr.ReadLine()) != null)
                    {
                        if (IsFirst == true)
                        {
                            tableHead = strLine.Split(',');
                            IsFirst = false;
                            columnCount = tableHead.Length;
                            //创建列
                            for (int i = 0; i < columnCount; i++)
                            {
                                DataColumn dc = new DataColumn(tableHead[i]);
                                dt.Columns.Add(dc);
                            }
                        }
                        else
                        {
                            aryLine = strLine.Split(',');
                            DataRow dr = dt.NewRow();
                            for (int j = 0; j < columnCount; j++)
                            {
                                dr[j] = aryLine[j];
                            }
                            dt.Rows.Add(dr);
                        }
                    }
                    if (aryLine != null && aryLine.Length > 0)
                    {
                        dt.DefaultView.Sort = tableHead[0] + " " + "asc";
                    }
                    //使用了Using可以不手动关闭了。好买书还是关一下的好
                    sr.Close();
                    fs.Close();
                }
            }
            catch (Exception ex)
            {

            }
            return dt;
        }

        /// <summary>
        /// 给定文件的路径，读取文件的二进制数据，判断文件的编码类型
        /// </summary>
        /// <param name="FILE_NAME">文件路径</param>
        /// <returns>文件的编码类型</returns>
        public static System.Text.Encoding GetType(string FILE_NAME)
        {
            FileStream fs = new FileStream(FILE_NAME, FileMode.Open,
              FileAccess.Read);
            System.Text.Encoding r = GetType(fs);
            fs.Close();
            return r;
        }

        /// <summary>
        /// 通过给定的文件流，判断文件的编码类型
        /// </summary>
        /// <param name="fs">文件流</param>
        /// <returns>文件的编码类型</returns>
        public static System.Text.Encoding GetType(FileStream fs)
        {
            byte[] Unicode = new byte[] { 0xFF, 0xFE, 0x41 };
            byte[] UnicodeBIG = new byte[] { 0xFE, 0xFF, 0x00 };
            byte[] UTF8 = new byte[] { 0xEF, 0xBB, 0xBF }; //带BOM
            System.Text.Encoding reVal = System.Text.Encoding.Default;

            BinaryReader r = new BinaryReader(fs, System.Text.Encoding.Default);
            int i;
            int.TryParse(fs.Length.ToString(), out i);
            byte[] ss = r.ReadBytes(i);
            if (IsUTF8Bytes(ss) || (ss[0] == 0xEF && ss[1] == 0xBB && ss[2] == 0xBF))
            {
                reVal = System.Text.Encoding.UTF8;
            }
            else if (ss[0] == 0xFE && ss[1] == 0xFF && ss[2] == 0x00)
            {
                reVal = System.Text.Encoding.BigEndianUnicode;
            }
            else if (ss[0] == 0xFF && ss[1] == 0xFE && ss[2] == 0x41)
            {
                reVal = System.Text.Encoding.Unicode;
            }
            r.Close();
            return reVal;
        }

        /// <summary>
        /// 判断是否是不带 BOM 的 UTF8 格式
        /// </summary>
        /// <param name="data"></param>
        /// <returns></returns>
        private static bool IsUTF8Bytes(byte[] data)
        {
            int charByteCounter = 1;  //计算当前正分析的字符应还有的字节数
            byte curByte; //当前分析的字节.
            for (int i = 0; i < data.Length; i++)
            {
                curByte = data[i];
                if (charByteCounter == 1)
                {
                    if (curByte >= 0x80)
                    {
                        //判断当前
                        while (((curByte <<= 1) & 0x80) != 0)
                        {
                            charByteCounter++;
                        }
                        //标记位首位若为非0 则至少以2个1开始 如:110XXXXX...........1111110X　
                        if (charByteCounter == 1 || charByteCounter > 6)
                        {
                            return false;
                        }
                    }
                }
                else
                {
                    //若是UTF-8 此时第一位必须为1
                    if ((curByte & 0xC0) != 0x80)
                    {
                        return false;
                    }
                    charByteCounter--;
                }
            }
            if (charByteCounter > 1)
            {
                throw new Exception("非预期的byte格式");
            }
            return true;
        }
    }
}

集合数据Model

/// <summary>
    /// 打标数据 Model
    /// </summary>
    public class MarkDataModel
    {
        /// <summary>
        /// 坐标X
        /// </summary>
        [Description("坐标X")]//可以自定义中文列名
        public double X { get; set; }

        /// <summary>
        /// 坐标Y
        /// </summary>
        public double Y { get; set; }

        /// <summary>
        /// 打标数据
        /// </summary>
        public string Text { get; set; }
    }