On 16 Dec 2009, at 10:18 AM, Eric E. Dolecki wrote:
> I am using NSUserDefaults to store some data. On first run of the
> application, I check for the data, and if it's not been set already, I set
> it.
This is done, and better, by -[NSUserDefaults registerDefaults:].
> I however get warnings in my code. In my .h I set up my variables, and then
> in my .m:
>
> NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
> alarm1_hour = [prefs integerForKey:@"alarm1Hour"];
> if( alarm1_hour == NULL ){
> NSLog(@"alarm 1 hour is null" );
> }
You don't say, but I assume (hope) that alarm1_hour is declared as an integer.
NULL is (at least notionally) declared as (void *)0; it's a pointer. Comparing
them is almost always a mistake. Code written after 1988 or so should not treat
integers and pointers as interchangeable.
Besides, -[NSUserDefaults integerForKey:] is documented (you read the
documentation?) to return 0 if the key doesn't appear in the user defaults.
Scalars (as in not-pointers) don't have "I'm not set" values (like NULL for
pointers); every possible value may be meaningful. You may have "sentinel"
values (valid, but you know to treat them as signals of a condition, rather
than in-band values), but that's another story.
> Should I use a temporary variable to check instead of the variable with the
> pointer? Or are these warnings okay to ignore?
You don't ignore warnings, except on the most serious consideration, such as
when the warning is about a condition that your code independently verifies
cannot happen.
— F
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