C#

<?xml version="1.0" encoding="utf-16"?>
<CategoryList a="12345" b="1d5458cd-a070-40cc-a3f4-cf3c394013cc" c="true" />

using System;
using System.Text;
using System.IO;
using System.Xml;

class Test
{
    public static void Main()
    {
        XmlDocument xmlDoc = new XmlDocument();


        // Write down the XML declaration
        XmlDeclaration xmlDeclaration = xmlDoc.CreateXmlDeclaration("1.0", "utf-8", null);

        // Create the root element
        XmlElement rootNode = xmlDoc.CreateElement("CategoryList");
        xmlDoc.InsertBefore(xmlDeclaration, xmlDoc.DocumentElement);
        // Set attribute name and value!
        rootNode.SetAttribute("a", "12345");
        rootNode.SetAttribute("b", Guid.NewGuid().ToString());
        rootNode.SetAttribute("c", "true");
        xmlDoc.AppendChild(rootNode);

        // Save to the XML file
        StringWriter stream = new StringWriter();
        xmlDoc.Save(stream);
        string content = stream.ToString();
        Console.Write(content);

        return;
    }
}