Geek asks and answers

What is the difference between these two listings?

Thus, in my travels, I saw how such transfers are listed (when a bit map is required)

enum {
    UIControlStateNormal       = 0,                       
    UIControlStateHighlighted  = 1 << 0,                  // used when UIControl isHighlighted is set
    UIControlStateDisabled     = 1 << 1,
    UIControlStateSelected     = 1 << 2,                  // flag usable by app (see below)
};

However, I recently looked at the NSJSONSerilization class to meet an enumeration defined as

enum {
    NSJSONReadingMutableContainers = (1UL << 0),
    NSJSONReadingMutableLeaves     = (1UL << 1),
    NSJSONReadingAllowFragments    = (1UL << 2)
};
typedef NSUInteger NSJSONReadingOptions;

So, I think my question is what it does UL. What is the difference between 1 << 1and1UL << 1

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4 answers

In C ++, ULjust means that a literal is an integer type unsigned long. Integer default literal int.

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1 << 1 1UL << 1, 1 << 33 1UL << 33. unsigned long , int, , enum , int .

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In practice, there is no difference in your code.

The type 1in the first is this int, and the type 1ULin the second is unsigned long.

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The code will work the same, there is no real difference.

However, the type is 1in the first code int, while the type is 1ULin the second code unsigned long.

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