objective c - Why does an NSInteger variable have to be cast to long when used as a format argument?

Question

NSInteger myInt = 1804809223;
NSLog(@"%i", myInt); <==== 

The code above produces an error:

Values of type 'NSInteger' should not be used as format arguments; add an explicit cast to 'long'?instead

The corrected NSLog message is actually NSLog(@"%lg", (long) myInt);. Why do I have to convert the integer value of myInt to long if I want the value to?display?

Answer 1

You get this warning if you compile on OS X (64-bit), because on that platform NSInteger is defined as long and is a 64-bit integer. The %i format, on the other hand, is for int, which is 32-bit. So the format and the actual parameter do not match in size.

Since NSInteger is 32-bit or 64-bit, depending on the platform, the compiler recommends to add a cast to long generally.

Update: Since iOS 7 supports 64-bit now as well, you can get the same warning when compiling for iOS.