Xcode warning: Format specifies type 'long' but the argument has type 'int _Nullable'

Question

I get this warning for the following line of code:

    NSLog(@"selected segment: %li", _segmentControl.selectedSegmentIndex);

The property selectedSegmentIndex is of type NSInteger.

If I change the format to %i i get the following warning:

Format specifies type 'int' but the argument has type 'long _Nullable'

Are there any new format specifiers for Nullable types or is this just a bug in Xcode 7?

Solution

You should type:

NSLog(@"selected segment: %li", (long)_segmentControl.selectedSegmentIndex);

Because NSInteger has a different length in 32 and 64bit architecture. Previously you didn't see the warning, because probably you was compiling only against 64 bit architecture.

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I'd also advise to read Apple Article, as there are new specifiers in Xcode 7 (among others nullable and nonnull).

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To answer your doubts from the comment, please refer to this Apple document, where they state the following:

Type Specifiers

Script action: Warns about potential problems; may generate false negatives.

Typically, in 32-bit code you use the %d specifier to format int values in functions such as printf, NSAssert, and NSLog, and in methods such as stringWithFormat:. But with NSInteger, which on 64-bit architectures is the same size as long, you need to use the %ld specifier. Unless you are building 32-bit like 64-bit, these specifiers generates compiler warnings in 32-bit mode. To avoid this problem, you can cast the values to long or unsigned long, as appropriate. For example:

NSInteger i = 34;
printf("%ld\n", (long)i);