Comparing Strings Efficiently

After doing some tests to measure the performance of StringBuilder, I started thinking about other ways strings are commonly used. What are some common inefficiencies, and how can I avoid them? Immediately I thought of evaluating strings.

I had previously seen comments on StackOverflow about ToUpper() being more efficient than ToLower(). I tried finding a source for this claim, but came up empty. The closest thing I found on the topic was an MSDN page pointing out that ToUpper() is more reliable that ToLower(), but nothing about performance.

In my own tests (full code here), I found there was no significant difference between ToUpper() and ToLower(). Thanks to one StackOverflow comment, I did discover that ToUpperInvariant() is slightly faster than ToLowerInvariant(), but not by much. With no major gains found comparing .ToUpper() and .ToLower(), it was time to compare strings like a real .NET developer.

StringComparison is the proper way to compare strings (bet you didn’t see that coming). Using .ToUpper() or .ToLower() creates another string in memory, while using StringComparison avoids that step allowing a much more efficient comparison.

string someString = "hello";
string otherString = "HELLO";
if (someString.Equals(otherString, StringComparison.OrdinalIgnoreCase))
   // they match

This code is 20 times faster than using ToUpper() or ToLower(). If this was a suprise to you or if you just want to check out other best practices, Microsoft has very thorough documentation discussing the different approaches for using strings in .NET.

About Me

Hi, I'm Dominic. I'm a software engineer working mostly with .NET Core and web technologies. Check out some of my projects, or get in touch.