Deprecated usage

The ConfigurationSettings class was the original way to retrieve settings for an assembly in .NET 1.0 and 1.1. It has been superseded by the ConfigurationManager class and the WebConfigurationManager class.

If you have two keys with the same name in the appSettings section of the configuration file, the last one is used.

app.config

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <appSettings>
    <add key="keyName" value="anything, as a string"/>
    <add key="keyNames" value="123"/>
    <add key="keyNames" value="234"/>
  </appSettings>
</configuration>

Program.cs

using System;
using System.Configuration;
using System.Diagnostics;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main()
        {
            string keyValue = ConfigurationSettings.AppSettings["keyName"];
            Debug.Assert("anything, as a string".Equals(keyValue));

            string twoKeys = ConfigurationSettings.AppSettings["keyNames"];
            Debug.Assert("234".Equals(twoKeys));

            Console.ReadKey();
        }
    }
}