Clear C# StringBuilder

Many .NET developers are baffled by the lack of a “Clear” method in the StringBuilder class.  For example, if you are using a StringBuilder in a loop, you may want to clear its contents at the beginning of each loop.

Options to Clear a StringBuilder

It turns out there are two common ways to clear a StringBuilder:
Option #1:  Create a new StringBuilder object

1	StringBuilder sb = new StringBuilder();

Option #2: Set its Length to zero

sb.Length = 0;

Which Option is Better?

Setting the Length property to zero is about 25% faster than creating a new StringBuilder object every time.
Option 2 seems intuitively better because it does not create a new object on the heap every time.  Even so, it’s not likely to make a noticeable performance difference in your software.  When looping a million times on a fast PC, setting the Length to zero is about 1 second faster than creating a new object.

Sample Console Program

Here is a simple console program that demonstrates this:

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using System; using System.Text;   namespace CSharp411 {     class Program     {         static void Main( string[] args )         {             int loops = 1000000;             int maxLength = 100;               DateTime time1 = DateTime.Now;             for (int i = 0; i < loops; i++)             {                 StringBuilder sb = new StringBuilder();                 for (int j = 0; j < maxLength; j++)                 {                     sb.Append( 'a' );                 }             }               DateTime time2 = DateTime.Now;             StringBuilder sb2 = new StringBuilder();             for (int i = 0; i < loops; i++)             {                 sb2.Length = 0;                 for (int j = 0; j < maxLength; j++)                 {                     sb2.Append( 'a' );                 }             }             DateTime time3 = DateTime.Now;               Console.WriteLine( "new = {0}, append = {1}", time2.Subtract( time1 ), time3.Subtract( time2 ) );             Console.ReadLine();         }     } }

The results of this program on my PC were:

new = 00:00:04.1050000, append = 00:00:03.0690000