Detecting (null) in Objective-C

Question

I want to detect whether passing a NSString to NSLog will return (null). I've tried if (string == @"") {do something}" and if (string == @"(null)") {do something}" but neither seem to work. Any advice would be greatly appreciated!

Those aren't comparisons; they're assignments. So they wouldn't work even if that were actually the right way to check for nil. — Chuck
– Chuck, Commented Jun 2, 2010 at 19:19

kevingessner · Accepted Answer · 2010-06-02 19:16:48Z

9

Your "NSString" is actually a pointer to an NSString (i.e. an NSString *). A null pointer in C is simply a pointer with the value 0; in C, 0 is false, so the following is simple and idiomatic:

NSString *str = ...;
if (str) {
    /// str is not null
}

(p.s.: Your comparisons with @"" and @"(null)" are comparing the addresses of the NSString pointers, not the values; to compare NSStrings, look at -isEqualToString:.)

answered Jun 2, 2010 at 19:16

kevingessner

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3 Comments

pxl Over a year ago

is there any reason to go one step further with: if (str===NULL)?

kevingessner Over a year ago

Well, C (and thus Objective-C) doesn't have a === operator, but you're free to use == or any other boolean operator. It's just not necessary, in the same way that writing if (some_bool == YES) is the same as if (some_bool), just with more characters.

dreamlax Over a year ago

@pxi: It is more idiomatic in Objective-C to compare objects to nil rather than NULL. They boil down to the same thing though.

Elfred · Accepted Answer · 2010-06-02 19:13:53Z

6

if (string == nil) {
   do_something;
}

answered Jun 2, 2010 at 19:13

Elfred

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