Question

Why is StringBuilder slower when compared to + concatenation?
StringBuilder was meant to avoid extra object creation, but why does it penalize performance?

    static void Main(string[] args)
    {
        int max = 1000000;
        for (int times = 0; times < 5; times++)
        {
            Console.WriteLine("\ntime: {0}", (times+1).ToString());
            Stopwatch sw = Stopwatch.StartNew();
            for (int i = 0; i < max; i++)
            {
                string msg = "Your total is ";
                msg += "$500 ";
                msg += DateTime.Now;
            }
            sw.Stop();
            Console.WriteLine("String +\t: {0}ms", ((int)sw.ElapsedMilliseconds).ToString().PadLeft(6));

            sw = Stopwatch.StartNew();
            for (int j = 0; j < max; j++)
            {
                StringBuilder msg = new StringBuilder();
                msg.Append("Your total is ");
                msg.Append("$500 ");
                msg.Append(DateTime.Now);
            }
            sw.Stop();
            Console.WriteLine("StringBuilder\t: {0}ms", ((int)sw.ElapsedMilliseconds).ToString().PadLeft(6));
        }
        Console.Read();
    }

EDIT: Moving out of scope variables as suggested:

Answer 1

Change so that the StringBuilder isn’t instantiated all the time, instead .Clear() it:

time: 1
String +    :   3348ms
StringBuilder   :   3151ms

time: 2
String +    :   3346ms
StringBuilder   :   3050ms

etc.

Note that this still tests exactly the same functionality, but tries to reuse resources a bit smarter.

Code: (also live on http://ideone.com/YuaqY)

using System;
using System.Text;
using System.Diagnostics;

public class Program
{
    static void Main(string[] args)
    {
        int max = 1000000;
        for (int times = 0; times < 5; times++)
        {
            {
                Console.WriteLine("\ntime: {0}", (times+1).ToString());
                Stopwatch sw = Stopwatch.StartNew();
                for (int i = 0; i < max; i++)
                {
                    string msg = "Your total is ";
                    msg += "$500 ";
                    msg += DateTime.Now;
                }
                sw.Stop();
                Console.WriteLine("String +\t: {0}ms", ((int)sw.ElapsedMilliseconds).ToString().PadLeft(6));
            }

            {
                Stopwatch sw = Stopwatch.StartNew();
                StringBuilder msg = new StringBuilder();
                for (int j = 0; j < max; j++)
                {
                    msg.Clear();
                    msg.Append("Your total is ");
                    msg.Append("$500 ");
                    msg.Append(DateTime.Now);
                }
                sw.Stop();
                Console.WriteLine("StringBuilder\t: {0}ms", ((int)sw.ElapsedMilliseconds).ToString().PadLeft(6));
            }
        }
        Console.Read();
    }
}