What does the question mark and the colon (?: ternary operator) mean in objective-c?

This is the C ternary operator (Objective-C is a superset of C): label. Frame = (inPseudoEditMode)? KLabelIndentedRect : kLabelRect is semantically equivalent to if(inPseudoEditMode) { label.

Frame = kLabelIndentedRect; } else { label. Frame = kLabelRect; }.

This is the C ternary operator (Objective-C is a superset of C): label. Frame = (inPseudoEditMode)? KLabelIndentedRect : kLabelRect; is semantically equivalent to if(inPseudoEditMode) { label.

Frame = kLabelIndentedRect; } else { label. Frame = kLabelRect; }.

Uhh that was fast :) Thanks a lot. – rdesign Apr 7 '10 at 19:47 2 (update: Yuck! Reposting as an answer.) What is so important about the ternary operator is that it can be used in places that an if-else cannot.

Ie: Inside a condition or method parameter. NSString stringWithFormat: @"Status: %@", (statusBool? @"Approved" : @"Rejected") ...which is a great use for preprocessor constants: #define statusString (statusBool?

@"Approved" : @"Rejected") ...then: NSString stringWithFormat: @"Status: %@", statusString This saves you from having to use and release local variables in if-else patterns. FTW! – Richard Bronosky May 6 '10 at 15:52.

It's the tertiary operator. It's basic form is: condition? ValueIfTrue : valueIfFalse Where the values will only be evaluated if they are chosen.

Building on Barry Wark's excellent explanation... What is so important about the ternary operator is that it can be used in places that an if-else cannot. Ie: Inside a condition or method parameter. NSString stringWithFormat: @"Status: %@", (statusBool?

@"Approved" : @"Rejected") ...which is a great use for preprocessor constants: // in your pch file... #define statusString (statusBool? @"Approved" : @"Rejected") // in your m file... NSString stringWithFormat: @"Status: %@", statusString This saves you from having to use and release local variables in if-else patterns. FTW!

This is part of C, so it's not Objective-C specific. Here's a translation into an if statement: if (inPseudoEditMode) label. Frame = kLabelIndentedRec; else label.

Frame = kLabelRect.

It's just a short form of writing an in-then-else statement. It means the same as the following code: if(inPseudoEditMode) label. Frame = kLabelIndentedRect else label.

Frame = kLabelRect.

That's just the usual ternary operator. If the part before the question mark is true, it evaluates and returns the part before the colon, otherwise it evaluates and returns the part after the colon. A?

B:c is like if(a) b; else c.

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