จำนวนความยาวของ string ตอนเป็น UTF-8 ไม่เท่ากับตอนเป็น ANSI ครับ

    string filePath = "c:\\test.txt";
     
    // Reads UTF8 file
    StreamReader fileStream = new StreamReader(filePath);
    string fileContent = fileStream.ReadToEnd();
    fileStream.Close();
     
    // Now writes the content in ANSI
    StreamWriter ansiWriter = new StreamWriter(filePath.Replace(".txt", "-ansi.txt"), false, Encoding.GetEncoding(1250));
    ansiWriter.Write(fileContent);
    ansiWriter.Close();

...
dim dread as SqlDataReader = cmd.ExecuteReader()
...

StreamWriter ansiWriter = new StreamWriter("test.txt", false, Encoding.GetEncoding(874))

dim sb as new System.Text.StringBuilder

Do While dread.read()
   sb.Clear()
   ...
   sb.AppendFormat("{0}{1}",dread("x1"),dread("x2"))
   ...
   ansiWriter.WriteLine(sb.ToString())
End While

ansiWriter.Close();

protected void ExportButton_Click(object sender, DirectEventArgs e)
        {
            string filename = "K" + Utils.Right(("0000000" + bibId),7) + ".txt";

            StringBuilder marc = new StringBuilder();
            marc.Append(GetVarField(bibId));
            
            //Download the Text file.
            Response.Clear();
            Response.AddHeader("content-disposition", "attachment;filename=" +  filename);
            Response.Charset = "";
            Response.ContentType = "application/vnd.text";
            //Response.ContentEncoding = System.Text.Encoding.Unicode;
            Response.Cache.SetCacheability(HttpCacheability.NoCache);
            System.IO.StringWriter stringWrite = new System.IO.StringWriter();
            System.Web.UI.HtmlTextWriter htmlWrite = new HtmlTextWriter(stringWrite);
            Response.Write(marc.ToString());
            Response.End();
        }        

        private string GetVarField(string bibId)
        {            
            char cRS = (char)30; // [RS] field terminator
            char cUS = (char)31; // [US] delimiter
            char cGS = (char)29; // [GS] record terminator 
            
            string marc = string.Empty;
            string directory = string.Empty;
            string varfield = string.Empty;

            { // get Variable Fields Value

                int tagStart = 0; // tag 001.Length + tag 003.Length              

                string queryString = "SELECT * FROM [BibTag_V] WHERE unUsed=0 AND bibId=" + bibId + " ORDER BY tag, tagId";
                string connectionString = strConn;
                using (SqlConnection connection = new SqlConnection(connectionString))
                {
                    SqlCommand command = new SqlCommand(queryString, connection);
                    command.Connection.Open();
                    command.ExecuteNonQuery();

                    SqlDataReader dt;
                    dt = command.ExecuteReader();

                    while (dt.Read())
                    {
                        string tag = dt["tag"].ToString();
                        string tagId = dt["tagId"].ToString();
                        bool isFullstop = bool.Parse(dt["isFullstop"].ToString());
                        string tagString = string.Empty;
                        directory += tag;

                        /* loop Subfield Value */                        
                        string querySf = "SELECT * FROM [BibSubfield_V] WHERE tagId=" + tagId + " ORDER BY tag, tagId, sorder";
                        using (SqlConnection conSf = new SqlConnection(connectionString))
                        {
                            SqlCommand commandSf = new SqlCommand(querySf, conSf);
                            commandSf.Connection.Open();
                            commandSf.ExecuteNonQuery();

                            SqlDataReader dtSf;
                            dtSf = commandSf.ExecuteReader();

                            while (dtSf.Read())
                            {
                                string sCode = dtSf["scode"].ToString();
                                string sValue = dtSf["svalue"].ToString();
                                string sPrefix = dtSf["prefixSymbol"].ToString();
                                string sOrder = dtSf["sorder"].ToString();
                                if (tag != "008")
                                {
                                    if (sOrder == "1")
                                    {   // add only cUS
                                        varfield += cUS;
                                        tagString += cUS;
                                    }
                                    else
                                    {   // add prefix & cUS
                                        if (!string.IsNullOrEmpty(sPrefix))
                                        {
                                            varfield += sPrefix + " ";
                                            tagString += sPrefix + " ";
                                        }                                        
                                        varfield += cUS;
                                        tagString += cUS;
                                    }                                
                                    varfield += sCode;
                                    tagString += sCode;
                                }                                
                                varfield += sValue;                                
                                tagString += sValue;
                            }

                            { // check last fullstop 
                                string ft = Utils.Right(tagString, 1);
                                if (ft != ".")
                                {
                                    if (isFullstop) 
                                    {
                                        varfield += ".";
                                        tagString += ".";                                     
                                    }
                                }                            
                            }

                            varfield += cRS;
                            tagString += cRS;
                            directory += Utils.Right("0000" + tagString.Length.ToString(), 4); // calculate length of field                            
                            directory += Utils.Right("00000" + tagStart.ToString(), 5); // calculate starting_chr_position
                            tagStart += int.Parse(tagString.Length.ToString());
                            tagString = string.Empty; // clear tagString to inital value
                            dtSf.Close();
                            dtSf = null;
                        } 
                                               

                    }
                    dt.Close();
                    dt = null;
                }

            }

            /* get Leader */
            int i0004 = 24 + int.Parse(directory.Length.ToString()) + 1 +int.Parse(varfield.Length.ToString()) + 1;
            // leader.l + directory.l + [RS] + varfield.l + [GS]
            string l0004 = Utils.Right("00000" + i0004.ToString(), 5);
            string l05 = "n";  // n == new
            string l06 = GetTypeOfRecord(bibId);
            string l07 = GetBibLevel(bibId);
            string l0811 = " a22"; // fixed value
            int i1216 = 24 + int.Parse(directory.Length.ToString()) + 1; 
            // leader.Length + directory.Length + [RS] 
            string l1216 = Utils.Right("00000" + i1216.ToString() , 5);
            string l1719 = " a "; // fixed value
            string l2023 = "4500"; // fixed value
            string leader = l0004 + l05 + l06 + l07 + l0811 + l1216 + l1719 + l2023;

            marc = leader + directory + cRS + varfield + cGS;
            return marc;

        }

public static System.Collections.Generic.List<string> textFileReaderFormline(string pathFileName)
        {

            System.Collections.Generic.List<string> list = new System.Collections.Generic.List<string>();
            System.IO.StreamReader fs;
            fs = new System.IO.StreamReader(pathFileName, System.Text.Encoding.GetEncoding(874));

            string line;
            while ((line = fs.ReadLine()) != null)
            {
                list.Add(line);
            }
            return list;

        }

    Protected Sub Page_Load(sender As Object, e As System.EventArgs) Handles Me.Load
        Dim sLine As String = "ข้าวมันไก่"
        Response.Clear()
        Response.ContentEncoding = Encoding.GetEncoding(874)
        Response.AddHeader("content-disposition", "attachment;filename=test.txt")
        Response.ContentType = "application/vnd.text"
        Response.Write(sLine)
        Response.End()
    End Sub

int tagStringLen = Encoding.UTF8.GetByteCount(tagString);
int directoryLen = Encoding.UTF8.GetByteCount(directory);
int varfieldLen = Encoding.UTF8.GetByteCount(varfield);