C# Cookbook

2.22. Improving StringBuilder Performance

Problem

In an attempt to improve string-handling performance, you have converted your code to use the StringBuilder class. However, this change has not improved performance as much as you had hoped.

Solution

The chief advantage of a StringBuilder object over a string object is that it preallocates a default initial amount of memory in an internal buffer in which a string value can expand and contract. When that memory is used, however, .NET must allocate new memory for this internal buffer. You can reduce the frequency with which this occurs by explicitly defining the size of the new memory using either of two techniques. The first approach is to set this value when the StringBuilder class constructor is called. For example, the code:

StringBuilder sb = new StringBuilder(200);

specifies that a StringBuilder object can hold 200 characters before new memory must be allocated.

The second approach is to change the value after the StringBuilder object has been created, using one of the following properties or methods of the StringBuilder object:

sb.Capacity = 200;
sb.EnsureCapacity(200);

Discussion

As noted in previous recipes in this chapter, the string class is immutable; once a string is assigned to a variable of type string, that variable cannot be changed in any way. So changing the contents of a string variable entails the creation of a new string containing the modified string. The reference variable of type string must then be changed to reference ...