Case insensitive comparison NSString

Question

if( [@"Some String" caseInsensitiveCompare:@"some string"] == NSOrderedSame ) {
  // strings are equal except for possibly case
}

The documentation is located at Search and Comparison Methods

 NSString *stringA;
 NSString *stringB;

 if (stringA && [stringA caseInsensitiveCompare:stringB] == NSOrderedSame) {
     // match
 }

Note: stringA && is required because when stringA is nil:

 stringA = nil;
 [stringA caseInsensitiveCompare:stringB] // return 0

and so happens NSOrderedSame is also defined as 0.

The following example is a typical pitfall:

 NSString *rank = [[NSUserDefaults standardUserDefaults] stringForKey:@"Rank"];
 if ([rank caseInsensitiveCompare:@"MANAGER"] == NSOrderedSame) {
     // what happens if "Rank" is not found in standardUserDefaults
 }

An alternative if you want more control than just case insensitivity is:

[someString compare:otherString options:NSCaseInsensitiveSearch];

Numeric search and diacritical insensitivity are two handy options.

You could always ensure they're in the same case before the comparison:

if ([[stringX uppercaseString] isEqualToString:[stringY uppercaseString]]) {
    // They're equal
}

The main benefit being you avoid the potential issue described by matm regarding comparing nil strings. You could either check the string isn't nil before doing one of the compare:options: methods, or you could be lazy (like me) and ignore the added cost of creating a new string for each comparison (which is minimal if you're only doing one or two comparisons).

A new way to do this. iOS 8

let string: NSString = "Café"
let substring: NSString = "É"

string.localizedCaseInsensitiveContainsString(substring) // true

- (NSComparisonResult)caseInsensitiveCompare:(NSString *)aString