Strings and performance

I really cannot stress enough importance of using StringBuilder class for string concatenation. The reason is obvious: PERFORMANCE! I know that most programmers are aware of the possible string concatenations performance problems but somehow this issue is still being overlooked and many make the mistake.The difference in performance between using and not using StringBuilder is HUGE as I'll show in simple demo application. I'm not saying that you should use StringBuilder for every string concatenation, but be very alert when you have loops that do string concatenation. Stop for a minute and think about possible performance issues. How much iteration do you expect your loop to have? If you loop through collection that you expect to get bigger and bigger over time, or a collection that you know nothing about (such as one coming from external system) then using StringBuilder has no alternative. Let's take a look how long does it take to do for example 30 000 string concatenations. by using StringBuilder. Code looks as follows :

class Program
  { 
      static void Main(string[] args) 
      { 
          StringBuilder sb = new StringBuilder(); 
          DateTime start = DateTime.Now;  
          for (int i = 0; i <30000; i++) 
          { 
              sb.Append("some string"); 
          } 
          TimeSpan ts = DateTime.Now - start;  
          Console.WriteLine("Finished!"); 
          Console.WriteLine(ts.TotalSeconds); 
          Console.ReadLine(); 
      } 
}

On my computer it takes exactly 0.15625 seconds which is very very fast.

Now let's take a look at same code but without using StringBuilder

 class Program
  { 
      static void Main(string[] args) 
      { 
          string str= string.Empty; 
          DateTime start = DateTime.Now;  
          for (int i = 0; i <30000; i++) 
          { 
              str+= "some string"; 
          } 
          TimeSpan ts = DateTime.Now - start;  
          Console.WriteLine("Finished!"); 
          Console.WriteLine(ts.TotalSeconds); 
          Console.ReadLine(); 
      } 
  }

Without StringBuilder it takes 21.396625 seconds.

Difference in performance is very noticeable and benefit of using StringBuilder is obvious. It's worth noting that performance issues are usually not discovered until system has been deployed and used in production, but by that time damage can already be done. That's why string concatenation must be taken with care.