What is the best was to determine if an NSString is empty? Right now I am using the following:
if (string == nil || [string isEqualToString:@""]) {
// do something }
Thanks for any advice.
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3 Answers
if ([string length] == 0) {
// do something
}
If the string is nil, then the message to nil will return zero, and all will still be well.
answered May 9, 2010 at 13:14
7 Comments
cocoafan
+1 for your answer. what about whitespaces? What if you don't want to count them? Any handy way?
John Calsbeek
@cocoafan Not concisely. If you need to do that frequently, I'd suggest adding a category to
NSString, something like isNotEmpty, that you can do your custom checks in. Then you can just do if ([string isNotEmpty]) { … } and it will also handle nils properly…
uchuugaka
You may still want to know why the length returned 0 so it might be useful sometimes to check for nil, after getting the zero.
uchuugaka
You would want to check against a temp string created by splitting the string with componentsSeparatedByCharactersInSet: [NSCharacterset whiteSpaceCharacterSet] then joining the resulting array of string components.
John Calsbeek
@Sulthan I completely agree with you, but being negative is important to this particular method, since messages to nil return
NO. Maybe hasValue or something of that sort would be better. |
This will not only check if there is nothing in the string but will also return false if it is just whitespace.
NSString *tempString = [myString stringByReplacingOccurrencesOfString:@" " withString:@""];
if ([tempString length] != 0) {
//There is something in the string.
} else {
//There is nothing or it is just whitespace.
}
3 Comments
uchuugaka
This only removes leading and trailing whitespace
Ken Thomases
Whatever else it might be,
-stringByReplacingOccurrencesOfString:withString: is not especially efficient. Much better to test what you're actually looking for: non-whitespace characters. !myString || [myString rangeOfCharacterFromSet:[[NSCharacterSet whitespaceCharacterSet] invertedSet].location == NSNotFound (In this case, you have to test whether myString is nil explicitly because an NSRange resulting from messaging nil won't have NSNotFound in its location field.)Not good solving
[nil length] is 0
(0==0) is 1
then ([string length] == 0) will be 1. Although it is wrong.
The best way is
if (![string length]) {
}
2 Comments
cocoafan
length is a NUMBER and should be checked with == 0. if(![string length]) is a c hack and (semantically) not correct since ! should be used for booleans. Please don't tell that it still works. I know that. It is just neanderthalish.