CODEWITHSUNDEEP
objective-cxcode
Bartłomiej Semańczyk
Bartłomiej Semańczyk

Reputation: 61774

What a single & means in objc syntax?

In code I found some lines:

UIApplication *application = [UIApplication sharedApplication]; //1
application.applicationIconBadgeNumber = 0; //2
UIUserNotificationSettings *currentSettings = application.currentUserNotificationSettings; //3
BOOL badgeAllowed = currentSettings.types & UIUserNotificationTypeBadge; //4

I know what mean lines 1 to 3, but what means line 4?

It returns BOOL but if I want both parts to be true there should be && instead of &. Why there is only one &? What does it mean? I would like to read some about it, but I do not know what is it.

Upvotes: 1

Views: 275

Answers (2)

Sulthan
Sulthan

Reputation: 130082

&& is a logical operator AND

& is a bitwise operator AND.

That means that every bit of the resulting number is set only if both operands have that bit set.

In this specific case

currentSettings.types

is a mask of allowed notification types (a bit is set for every type). ANDing it with UIUserNotificationTypeBadge results in

  1. If UIUserNotificationTypeBadge is part of the mask, only that specific bit is set in the result.
  2. If UIUserNotificationTypeBadge is not part of the mask, the result has all bits set to zero.

Then the integer is considered as a boolean, which means non-zero = true, zero = false.

The last step can be written explicitly (which is better IMHO)

BOOL badgeAllowed = ((currentSettings.types & UIUserNotificationTypeBadge) != 0);

Upvotes: 2

sbooth
sbooth

Reputation: 16966

& is the C bitwise AND operator. It compares each bit of the left and right operands and set the corresponding result bit to 1 if the source bits are both 1 and 0 otherwise. For your code, the bit mask UIUserNotificationTypeBadge is used to check whether that individual bit is set in currentSettings.types. In C all non-zero values are interpreted as true so if currentSettings.types has the UIUserNotificationTypeBadge bit set badgeAllowed will be true, although not necessarily 1.

Upvotes: 0

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