将 dd.mm.yyyy 转换为 c# 中 .csv 文件中的 yyyy-mm-dd

Question

I have a CSV file like this:

abc;30.11.2021;xyz

I need to convert the date value to this format:

abc;2021-11-30;xyz

any ideas for that?

Currenty I do this:

//config Ini auslesen für Quell- und Zieldatei
        var dic = File.ReadAllLines("config.ini")
          .Select(l => l.Split(new[] { '=' }))
          .ToDictionary(s => s[0].Trim(), s => s[1].Trim());
        //Wert für Quelle
        string source = dic["source"];
        //Wert für das Ziel
        string target = dic["target"];

        string filePath = source ;

        var csv = File
        .ReadLines(source)
        .Select((line, index) => index == 0
           ? line + ";ExtID"                                     // Neue Kopfzeile
           : line + ";" + string.Concat(line.Split(';').Take(2)) // Spalte 1 + 2 in neue Spalte einfügen
         )
        .ToList();

        File.WriteAllLines(target, csv);

So I read an csv file, add a column and fill this column but to be honnest I don't know how to convert the date value.

Answer 1

use ParseExact to convert the string to DateTime and use ToString to convert back to the desired format

var s = DateTime.ParseExact("30.11.2021", "dd.MM.yyyy", CultureInfo.InvariantCulture).ToString("yyyy-MM-dd");
Console.WriteLine(s);

Answer 2

Something like this:

using (System.IO.StreamWriter writer = new System.IO.StreamWriter("newfile.csv"))
 {
     foreach (string line in System.IO.File.ReadAllLines("oldfile.csv"))
     {
         string[] items = line.Split(new[] { ';' });

         string newDateFormat = DateTime.ParseExact(items[1], "dd.MM.yy", System.Globalization.CultureInfo.CurrentCulture).ToString("yyyy-MM-dd");

         writer.Write(items[0]);
         writer.Write(';');
         writer.Write(newDateFormat);
         writer.Write(';');
         writer.Write(items[2]);
         writer.Write(';');
         writer.WriteLine();
     }
 }

Replace "oldfile.csv" with the input file and the output will be saved to "newfile.csv".