.Net: String vs. StringBuilder

When handling strings in .NET, it's known that it's "usually more efficient" to use StringBuilder.Append than String + String. However, using StringBuilder sacrifices a (small) amount of code readability, and creating a new StringBuilder() requires a certain amount of processor time in itself. So when is that trade off in efficiency worth it, and when is it best to stick with using a simple String + String?

.Net String vs. StringBuilder - concatenation performance discusses this in a fair amount of detail. The article is a couple of years old now (August 2004), but it's well written and contains code snippets as well as graphs to back up the findings.

The summary points of the findings:

If you have no idea on the resulting string size, use StringBuilder if you have at least 7 concatenations.

If you can roughly (with 30% accuracy) estimate the resulting string size, use StringBuilder if you have at least 5 concatenations.

If you can estimate the resulting string size with good accuracy, use StringBuilder if you have at least 3 concatenations.

Under no conditions is StringBuilder faster for less than 3 concatenations.

StringBuilder beats strings for 10+ concatenations in every practical situation.

The longer the strings are, the more final string size estimations will help you (but accuracy becomes more critical).

Further, he concludes:

StringBuilder performance is a tricky thing. In the last chapter you saw that the StringBuilder with perfect size estimation can be 15 times faster than normal string concatenation. But earlier in the article you also saw that even the default StringBuilder beats normal string catenation by a clear marginal once the cutoff point of 4-8 concatenations is passed. Except for the most critical string handling loops, optimizing the process to the point of making perfect estimations isn't usually worth it. For reasons of code clarity you might even want to avoid using StringBuilder when the amount of concatenations is only slightly over the cutoff point and you're working with an operation that's not critical to the millisecond level. For example, constructing a ten-part SQL statement is likely to be faster with StringBuilder, but the speed difference is negligible when compared to the execution time of that statement. Though, once you become familiar with the StringBuilder class, you'll be reading sb.Appends just like you read plus signs.

Useful reading for anyone looking to do some performance tuning on a string heavy app.

 Print | Posted on Friday, November 24, 2006 2:53 PM |