Comparing two strings, ignoring case in 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!

The first one is the correct one, and IMHO the more efficient one, since the second 'solution' instantiates a new string instance.

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.