修饰符标志：NSInteger是否足够？

Question

Is an NSInteger enough to keep track of a modifier flags? (cmd / alt / ctrl etc).

I notice that on an event it returns an NSUinteger (unsigned) ([theEvent modifierFlags]) instead of an NSInteger, but from my testing it appears to be working just fine when I save the modifier mask in an NSInteger.

I need an NSInteger because I'm saving the modifier mask as the tag of certain controls.

Answer 1

NSInteger and NSUInteger are the same size (ie. same number of bits). The difference is whether the bits are considered to represent a signed or unsigned number when performing arithmetic, etc. If you're only ever manipulating the number with bitwise operations, it won't really matter. That said, you should use the same type that the method in question returns, in this case NSUInteger. The reason for using an unsigned here is that when the value in question is really a bunch of bits to be set/cleared independently, it doesn't make sense conceptually for that value to have a sign bit.

Answer 2

As Andrew said, i just want to add something. If you are using bitflags as it seems from your question in iOS 6 they introduced a new macro, that seems the new "Apple way"

typedef NS_OPTIONS(NSInteger, CustomType) {
    kCmdKey = 1 << 0,
    kAltKey = 1 << 1,
    ctrlKey = 1 << 2,
};

there is also a macro NS_ENUM, for enums that are not used as bitmasks. in both NS_OPTIONS and NS_ENUM you can specify the type to use (NSInteger) and your typedef type name.