CODEWITHSUNDEEP
iosobjective-cmacros
Segev
Segev

Reputation: 19303

Trying to understand the operation sequence of macros

#define IS_IPHONE5 (([[UIScreen mainScreen] bounds].size.height-568)?NO:YES)
#define HEIGHT IS_IPHONE5 ? 568 : 480

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@"HEIGHT: %d",HEIGHT);
    NSLog(@"HEIGHT: %d",HEIGHT+99);
}

Both of the logs above will result 568. I'm guessing this is happening because of the sequence of the operations. Can any one give me a good explanation on this?

(I'm not looking for a solution or an alternative way doing the above. Just an explanation why this is happening)

Upvotes: 0

Views: 55

Answers (2)

Midhun MP
Midhun MP

Reputation: 107231

This

NSLog(@"hight: %d",HIGHT+99);

Will expand as

 NSLog(@"hight: %d",IS_IPHONE5 ? 568 : 480+99);

and then

NSLog(@"hight: %d",(([[UIScreen mainScreen] bounds].size.height-568)?NO:YES) ? 568 : 480+99);

So it will yield 568

Solutions:

NSLog(@"hight: %d",(HIGHT)+99);

or

#define HIGHT (IS_IPHONE5 ? 568 : 480)

I'll suggest to use second solution.

Upvotes: 2

rmaddy
rmaddy

Reputation: 318934

Macros like you have are simply replaced at compile time. Once your code is compiled, the code is just:

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@"hight: %d",(([[UIScreen mainScreen] bounds].size.height-568)?NO:YES) ? 568 : 480);
    NSLog(@"hight: %d",(([[UIScreen mainScreen] bounds].size.height-568)?NO:YES) ? 568 : 480+99);
}

Upvotes: 1

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