问题
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What is difference between different string compare methods
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\")
?
回答1:
The first one is the correct one, and IMHO the more efficient one, since the second 'solution' instantiates a new string instance.
回答2:
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!
回答3:
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.
回答4:
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.
回答5:
I'd venture that the safest is to use String.Equals to mitigate against the possibility that val is null.
回答6:
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.
回答7:
1st is more efficient (and the best possible option) because val.ToLowerCase() creates a new object since Strings are immutable.
回答8:
you may also want to look at that already answered question Differences in string compare methods in C#
来源：https://stackoverflow.com/questions/6371150/comparing-two-strings-ignoring-case-in-c-sharp