Cocoa:NSUInteger vs unsigned int When the Range is Very Small?

I hav开发者_运维问答e an unsigned int variable and it can only have the values of 0 -> 30. What should I use: unsigned int or NSUInteger? (for both 32 and 64 bit)

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I’d go with either NSUInteger (as the idiomatic general unsigned integer type in Cocoa) or uint8_t (if size matters). If I expected to be using 0–30 values in several places for the same type of data, I’d typedef it to describe what it represents.

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Running this:

    int sizeLong = sizeof(unsigned long);
    int sizeInt = sizeof(unsigned int);
    NSLog(@"%d, %d", sizeLong, sizeInt);

on 64bits gives: 8, 4 on 32 bits gives: 4, 4 So that yes, on 64 bits unsigned long (NSUInteger) takes twice as much memory as NSUInteger on 32 bits.

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It makes very little difference in your case, there is no right or wrong. I might use an NSUInteger, just to match with Cocoa API stuff.

NSUInteger is defined like this:

#if __LP64__ || TARGET_OS_EMBEDDED || TARGET_OS_IPHONE || TARGET_OS_WIN32 || NS_BUILD_32_LIKE_64
typedef long NSInteger;
typedef unsigned long NSUInteger;
#else
typedef int NSInteger;
typedef unsigned int NSUInteger;
#endif

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When u really want to use some of the unsigned type, choosing between unsigned int and NSUInteger does not matter because those types are equal(comparing the range and size in 32 & 64 bit). The same applies to int and NSInteger:

#if __LP64__ || (TARGET_OS_EMBEDDED && !TARGET_OS_IPHONE) || TARGET_OS_WIN32 || NS_BUILD_32_LIKE_64
typedef long NSInteger;
typedef unsigned long NSUInteger;
#else
typedef int NSInteger;
typedef unsigned int NSUInteger;
#endif

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Personally, I have just been bitten by this choice. I went down the NSUInteger route and have just spent HOURS looking into an obscure bug.

I had code that picked a random number and returned an NSUInteger. The code for the relied on the overflow of the number. However I did not anticipate that the size of the number varied between 32bit and 64bit systems. The rest of my code assumed (incorrectly) that the number would be up to 32 bit in size. The result is the code worked perfectly under 32 bit devices, but on iPhone 5S, it all fell apart.

There is nothing wrong with using NSUInteger, however its worth remembering that the number range is significantly higher so factor this dynamicism into any maths you do with that number.