using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

using System.Collections.ObjectModel;

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

using CsvHelper;

using CsvHelper.Configuration;

using CsvHelper.Configuration.Attributes;

using CsvHelper.Expressions;

using CsvHelper.TypeConversion;

​

//https://stackoverflow.com/questions/67216668/write-data-in-specific-position

​

    class Dto

    {

        public string Data1 { get; set; }

        public string DataN { get; set; }

        public string DataN1 { get; set; }

    }

​

    class DtoMap : ClassMap<Dto>

    {

        const int N = 12;

        public DtoMap() : this(true) { }

        public DtoMap(bool includeEmptyColumns)

        {

            Map(x => x.Data1).Index(0);

​

            if (includeEmptyColumns)

            {

                for (int i = 1; i < N; i++)

                {

                    Map().Index(i).Constant("").Name($"Column {i}");

                }

            }

​

            // Note that I need to skip N columns

            Map(x => x.DataN).Index(N);

            Map(x => x.DataN1).Index(N + 1);

        }

    }

​

    class TestClass

    {

        static byte [] CreateCSV<TMap, TRecords>(IEnumerable<TRecords> records, CsvConfiguration csvConfiguration) where TMap : ClassMap<TRecords>

        {

            using (var memoryStream = new MemoryStream())

            using (var streamWriter = new StreamWriter(memoryStream))

            using (var csvWriter = new CsvWriter(streamWriter, csvConfiguration))

            {

                csvWriter.Context.RegisterClassMap<TMap>();

                csvWriter.WriteRecords(records);

                streamWriter.Flush();

​

                return memoryStream.ToArray();

            }

        }

​

        static List<TRecords> ReadCSV<TRecords>(byte [] data, ClassMap<TRecords> map, CsvConfiguration csvConfiguration)

        {

            using (var memoryStream = new MemoryStream(data))

            using (var streamWriter = new StreamReader(memoryStream))

            using (var csvReader = new CsvReader(streamWriter, csvConfiguration))

            {

                csvReader.Context.RegisterClassMap(map);

                return csvReader.GetRecords<TRecords>().ToList();

            }

        }

        public static void Test()

        {

            var records = new []

            {

                new Dto

                {

                    Data1 = "data 1",

                    DataN = "data N",

                    DataN1 = "data N + 1"

                },

            };

            var config = new CsvConfiguration(CultureInfo.InvariantCulture);

            var csv = CreateCSV<DtoMap, Dto>(records, config);

            Console.WriteLine(Encoding.UTF8.GetString(csv));

            var newRecords = ReadCSV(csv, new DtoMap(false), config);

​

            var csv2 = CreateCSV<DtoMap, Dto>(newRecords, config);

            Console.WriteLine(Encoding.UTF8.GetString(csv2));

        }   

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1})", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , GetNetCoreVersion());

            Console.WriteLine("CsvHelper: " + typeof(CsvConfiguration).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

        public static string GetNetCoreVersion()

        {

            //https://techblog.dorogin.com/how-to-detect-net-core-version-in-runtime-ecd65ad695be

            //

            var assembly = typeof(System.Runtime.GCSettings).GetTypeInfo().Assembly;

            var assemblyPath = assembly.CodeBase.Split(new[] { '/', '\\' }, StringSplitOptions.RemoveEmptyEntries);

            int netCoreAppIndex = Array.IndexOf(assemblyPath, "Microsoft.NETCore.App");

            if (netCoreAppIndex > 0 && netCoreAppIndex < assemblyPath.Length - 2)

                return assemblyPath[netCoreAppIndex + 1];

            return null;

        }

    }

​