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

objective-c c syntax operators conditional-operator
danielreiser picture danielreiser · Apr 7, 2010 · Viewed 339.3k times · Source

What does this line of code mean?

label.frame = (inPseudoEditMode) ? kLabelIndentedRect : kLabelRect;

The ? and : confuse me.

Answer

Barry Wark picture Barry Wark · Apr 7, 2010

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;
}

The ternary with no first element (e.g. variable ?: anotherVariable) means the same as (valOrVar != 0) ? valOrVar : anotherValOrVar

Related questions

How to split a string literal across multiple lines in C / Objective-C?

I have a pretty long sqlite query: const char *sql_query = "SELECT statuses.word_id FROM lang1_words, statuses WHERE statuses.word_id = lang1_words.word_id ORDER BY lang1_words.word ASC"; How can I break it in a …

Read More
Objective-C : BOOL vs bool

I saw the "new type" BOOL (YES, NO). I read that this type is almost like a char. For testing I did : NSLog(@"Size of BOOL %d", sizeof(BOOL)); NSLog(@"Size of bool %d", sizeof(bool)); Good to see that …

Read More
How do I define and use an ENUM in Objective-C?

I declared an enum in my implementation file as shown below, and declared a variable of that type in my interface as PlayerState thePlayerState; and used the variable in my methods. But I am getting errors stating that it is …

Read More