Definition of bit masks in objective-c -


i learning objective-c , can't understand bitmasks, can me understand please? , don't know function of operator << is.

objective c existing of c, , uses same bitwise operators. lets take uiremotenotificationtype example:

uiremotenotificationtypenone    = 0, uiremotenotificationtypebadge   = 1 << 0, uiremotenotificationtypesound   = 1 << 1, uiremotenotificationtypealert   = 1 << 2, uiremotenotificationtypenewsstandcontentavailability = 1 << 3,

the << shift left operator , function obvious once @ binary form:

1 << 0 = 1 (decimal) = 0000001 (binary) 1 << 1 = 2 (decimal) = 0000010 (binary) 1 << 2 = 4 (decimal) = 0000100 (binary) 1 << 3 = 8 (decimal) = 0001000 (binary)

it shifts specific pattern (the left operand) left, 'length' of shift determined right operand. works other numbers 1; 3 << 2 = 12 because 0000011 (binary) shifted 2 places 0001100. translated normal mathematics, a << b = * 2^b.

the specific use of pattern is easy check if option set. suppose want application send notifications badges , alerts. pass value uiremotenotificationtypebadge | uiremotenotificationtypealert api, is

uiremotenotificationtypebadge = 0000001 uiremotenotificationtypealert = 0000100                         total = 0000101 |

(the | bitwise or operator; every bit, result 1 if 1 or both of corresponding bit of operands 1). api can check if badge property present & operator:

                        total = 0000101 uiremotenotificationtypebadge = 0000001                        result = 0000001 &

(the & bitwise , operator; every bit, result 1 if both of corresponding bit of operands 1). result non-zero, badge property present. let's same sound property:

                        total = 0000101 uiremotenotificationtypesound = 0000010                        result = 0000000 &

the result zero, badge property not present.


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