Comparing two strings, ignoring case in C#
C#StringComparisonEqualsC# Problem Overview
Which of the following two is more efficient? (Or maybe is there a third option that's better still?)
string val = "AStringValue";
if (val.Equals("astringvalue", StringComparison.InvariantCultureIgnoreCase))
OR
if (val.ToLowerCase() == "astringvalue")
?
C# Solutions
Solution 1 - C#
If you're looking for efficiency, use this:
string.Equals(val, "astringvalue", StringComparison.OrdinalIgnoreCase)
Ordinal comparisons can be significantly faster than culture-aware comparisons.
ToLowerCase can be the better option if you're doing a lot of comparisons against the same string, however.
As with any performance optimization: measure it, then decide!
Solution 2 - C#
The first one is the correct one, and IMHO the more efficient one, since the second 'solution' instantiates a new string instance.
Solution 3 - C#
The .ToLowerCase version is not going to be faster - it involves an extra string allocation
(which must later be collected), etc.
Personally, I'd use
string.Equals(val, "astringvalue", StringComparison.OrdinalIgnoreCase)
this avoids all the issues of culture-sensitive strings, but as a consequence it avoids all the issues of culture-sensitive strings. Only you know whether that is OK in your context.
Using the string.Equals static method avoids any issues with val being null.
Solution 4 - C#
My general answer to this kind of question on "efficiency" is almost always, which ever version of the code is most readable, is the most efficient.
That being said, I think (val.ToLowerCase() == "astringvalue") is pretty understandable at a glance by most people.
The efficience I refer to is not necesseraly in the execution of the code but rather in the maintanance and generally readability of the code in question.
Solution 5 - C#
I'd venture that the safest is to use String.Equals to mitigate against the possibility that val is null.
Solution 6 - C#
The former is fastest. Turns out that val is immutable, and so a new string object is created with String.ToLowerCase(), rather than just direct comparison with the string comparer. Creating a new string object can be costly if you're doing this many times a second.
Solution 7 - C#
you may also want to look at that already answered question https://stackoverflow.com/questions/44288/differences-in-string-compare-methods-in-c/44373#44373
Solution 8 - C#
1st is more efficient (and the best possible option) because val.ToLowerCase() creates a new object since Strings are immutable.