String comparison in Objective-C

Question

I've currently got a webserver set up which I communicate over SOAP with my iPhone app. I am returning a NSString containing a GUID and when I attempt to compare this with another NSString I get some strange results.

Why would this not fire? Surely the two strings are a match?

NSString *myString = @"hello world";

if (myString == @"hello world")
    return;

http://stackoverflow.com/questions/3703554/understanding-nsstring-comparison Nicely answered here as well. — Emile, Feb 19 '14 at 11:37

score 251 · Accepted Answer · answered Apr 07 '10 at 12:54

251

Use the -isEqualToString: method to compare the value of two strings. Using the C == operator will simply compare the addresses of the objects.

if ([category isEqualToString:@"Some String"])
{
    // Do stuff...
}

answered Apr 07 '10 at 12:54

jlehr

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AH! Thanking you muchly. Feel like a bit of a fool on this one! – ingh.am Apr 07 '10 at 13:05
4

My guess is that in ObjectiveC++ you could create an operator overload to give you syntactically-sugary ability to use == but no sane objective C programmer would do this, because == is only used for identity checks in objective C objects. – Warren P Apr 07 '10 at 18:26

score 54 · Answer 2 · edited Nov 13 '12 at 10:34

54

You can use case-sensitive or case-insensitive comparison, depending what you need. Case-sensitive is like this:

if ([category isEqualToString:@"Some String"])
{
   // Both strings are equal without respect to their case.
}

Case-insensitive is like this:

if ([category compare:@"Some String" options:NSCaseInsensitiveSearch] == NSOrderedSame)
{
   // Both strings are equal with respect to their case.
}

edited Nov 13 '12 at 10:34

JJD

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answered Apr 07 '10 at 14:39

mxg

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I think it should be: ([category compare:@"Some String" options:NSCaseInsensitiveSearch] == NSOrderedSame) – JaakL Jun 14 '12 at 13:33
11

Be careful with the "compare" function because if the string (in this case "category") is nil, compare will always return NSOrderedSame. – nh32rg Jul 26 '13 at 15:21
That's a great point @nh32rg!! +1 for that! Does the isEqualToString have the same problem? – badweasel Aug 28 '14 at 21:56

score 5 · Answer 3 · answered Apr 04 '15 at 08:00

You can compare string with below functions.

NSString *first = @"abc";
NSString *second = @"abc";
NSString *third = [[NSString alloc] initWithString:@"abc"];
NSLog(@"%d", (second == third))  
NSLog(@"%d", (first == second)); 
NSLog(@"%d", [first isEqualToString:second]); 
NSLog(@"%d", [first isEqualToString:third]); 

Output will be :-
    0
    1
    1
    1

String comparison in Objective-C

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