What is the best way to check if two strings are the same but ignore case?

Question

If I have two strings and want to check if they are the same, is something like this OK? 

string1.ToLower() == string2.ToLower()

So just tolowering both or I guess converting to uppercase as well?

Answer 1

Actually, the best way would be to use the string equals method. You can do this on an existing string like so : 

var string1 = "hello";
var string2 = "world";
string1.Equals(string2, StringComparison.InvariantCultureIgnoreCase);

But a better way might be to use the static String equals method because it can handle scenarios like this : 

string string1 = null;
var string2 = "world";
string.Equals(string1, string2, StringComparison.InvariantCultureIgnoreCase);

The reason you don't want to just ToLower is for a couple of reasons : 

• In some languages, ToLower might not give you what you expect (e.g. Characters from other languages)
• If one of the values is null, then calling ToLower() will throw an exception (Although this is easily avoidable, it's still a consideration)
• But the biggest issue is that when you call ToLower() you are actually creating a new string in memory just to compare the values. On smaller strings you might not notice it but it can add up very quickly to performance bottlenecks on large strings.