NSNotFound

NSNotFound is a constant in Apple's Foundation and related Cocoa frameworks used as a sentinel value to indicate that a requested item or index could not be found. It is most commonly associated with methods that return a numeric location, such as NSString rangeOfString: or rangeOfCharacterFromSet:, where a location equal to NSNotFound signals that the search term was not found.

Value and type: NSNotFound is defined as NSIntegerMax, the maximum value for the NSInteger type. On 64-bit platforms this corresponds to 9223372036854775807, and on 32-bit platforms it is 2147483647. Although location values in many APIs are unsigned, the sentinel uses the signed NSIntegerMax, so comparisons typically test for r.location == NSNotFound rather than -1.

Practical usage: In Objective-C, a common pattern is to perform a search and then check the location field against NSNotFound to determine whether the search succeeded. For example, NSString *s = ...; NSRange r = [s rangeOfString:@"foo"]; if (r.location == NSNotFound) { /* not found */ }. When bridging to Swift, optionals are often used instead of NSNotFound, though some older APIs may still expose the sentinel value.

Notes: NSNotFound represents a not-found condition and is not a valid index. Not every API uses NSNotFound; some return error codes or different indicators. Developers should consult the specific API documentation to understand whether and how NSNotFound is used as a sentinel value in that context.