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Some questions about bitwise operators

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By User


I read about bitwise operators today and they seem rather handy to me. I also noticed Apple uses them too, for example with UIViewAutoresizing .



In my app I need to keep track of the seven days of the week. Each day can be either enabled or disabled. I used to have seven BOOL 's, but now I'm trying to use a single integer for this: 





enum {

    DaysMonday = 1 << 0,

    DaysTuesday = 1 << 1,

    DaysWednesday = 1 << 2,

    DaysThursday = 1 << 3,

    DaysFriday = 1 << 4,

    DaysSaturday = 1 << 5,

    DaysSunday = 1 << 6

};

typedef NSUInteger Days;


My question is, how can I enable/disable those values now? I know I can check a variable days for a specific day like this: 





if (days & DaysThursday) {

    // thursday enabled

}


But how do I..



  1. enable thursday?

  2. disable thursday?

  3. toggle thursday?

  4. enable all?

  5. disable all?



Thank you.


Source: Tips4all, CCNA FINAL EXAM
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Comments

  1. UserMay 14, 2012 at 9:15 AM

    I'm not too familiar with objective-c, but here are the basics when dealing with bitwise operators.

    Enable Thursday

    days = days | DaysThursday;


    Disable Thursday

    allDays = DaysMonday | DaysTuesday | ... | DaysSunday;
    days = days & (allDays ^ DaysThursday);
    // OR
    days = days & ~DaysThursday;


    Toggle Thursday

    days = days ^ DaysThursday;


    Enable All

    allDays = DaysMonday | DaysTuesday | ... | DaysSunday;
    days = days | allDays;
    // OR
    days = allDays;


    Disable All

    days = days ^ days;
    // OR
    days = 0;

    ReplyDelete
  2. UserMay 14, 2012 at 9:15 AM

    days = DaysMonday | DaysWednesday | DaysFriday | DaysSaturday;
    days = days | DaysThursday;
    days = days & ~DaysSaturday;

    ReplyDelete

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