using System;

using System.Collections.Generic;

using System.Text;

using System.Linq;

using System.Xml.Serialization;

using System.Xml;

using System.Xml.Linq;

using System.IO;

​

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

​

//https://stackoverflow.com/questions/72348095/conversion-of-the-special-characters-while-adding-it-to-the-xml-innertext-in-c-s

​

    public class TestClass

    {

        public static void Test()

        {

            // Construct your XmlDocument (not shown in the question)

            var xmlDoc = new XmlDocument();

            xmlDoc.LoadXml("<Root></Root>");

            var eqnPartElm = xmlDoc.CreateElement("inf");

            xmlDoc.DocumentElement.AppendChild(eqnPartElm);

            // Add some non-ASCII text (here – is an En Dash character).

            eqnPartElm.InnerText = "–CO–OR";

​

            // Output to XML and escape all non-ASCII characters.

            var xml = xmlDoc.GetOuterXml(indent : true, encoding : Encoding.ASCII, omitXmlDeclaration : true);

            Console.WriteLine(xml);

​

            var fileName = "Question72348095.xml";

            using (var stream = new FileStream(fileName, FileMode.OpenOrCreate))

            {

                xmlDoc.Save(stream, indent : true, encoding : Encoding.ASCII);

            }

            Console.WriteLine(File.ReadAllText(fileName));

        }

    }

​

    public static class XmlSerializationHelper

    {

        public static string GetOuterXml(this XmlNode node, bool indent = false, Encoding encoding = null, bool omitXmlDeclaration = false)

        {

            if (node == null)

                return null;

            using var stream = new MemoryStream();

            node.Save(stream, indent : indent, encoding : encoding, omitXmlDeclaration : omitXmlDeclaration, closeOutput : false);

            stream.Position = 0;

            using var reader = new StreamReader(stream);

            return reader.ReadToEnd();

        }

        public static void Save(this XmlNode node, Stream stream, bool indent = false, Encoding encoding = null, bool omitXmlDeclaration = false, bool closeOutput = true) =>

            node.Save(stream, new XmlWriterSettings

                      {

                          Indent = indent,

                          Encoding = encoding,

                          OmitXmlDeclaration = omitXmlDeclaration,

                          CloseOutput = closeOutput,

                      });

​

        public static void Save(this XmlNode node, Stream stream, XmlWriterSettings settings)

        {

            using (var xmlWriter = XmlWriter.Create(stream, settings))

            {

                node.WriteTo(xmlWriter);

            }

        }

    }

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: {0} ({1}, {2})", System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription , Environment.Version, Environment.OSVersion);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

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

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​