[c#] Comparing two strings, ignoring case in C#

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")

?

I'd venture that the safest is to use String.Equals to mitigate against the possibility that val is null.

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.

1st is more efficient (and the best possible option) because val.ToLowerCase() creates a new object since Strings are immutable.

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.

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.

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!

you may also want to look at that already answered question Differences in string compare methods in C#