利用windows系統自帶的kernel32.dll檔案，然後將其引入到自己的專案中來，就可以輕鬆實現獲取計算機全名了，好了直接上程式碼

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;

namespace Name
{
    class Program
    {
        enum COMPUTER_NAME_FORMAT
        {
            ComputerNameNetBIOS,
            ComputerNameDnsHostname,
            ComputerNameDnsDomain,
            ComputerNameDnsFullyQualified,
            ComputerNamePhysicalNetBIOS,
            ComputerNamePhysicalDnsHostname,
            ComputerNamePhysicalDnsDomain,
            ComputerNamePhysicalDnsFullyQualified
        }

        [DllImport("kernel32.dll")]
        static extern bool GetComputerNameEx(COMPUTER_NAME_FORMAT NameType, StringBuilder lpBuffer, ref uint lpnSize);

        static void Main(string[] args)
        {
            bool success;
            StringBuilder name = new StringBuilder(100);
            uint size = 100;
            success = GetComputerNameEx(COMPUTER_NAME_FORMAT.ComputerNamePhysicalDnsFullyQualified, name, ref size);
            Console.WriteLine(name.ToString()); 
        }
    }
}