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PONSCalendar problem with BC era
 

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  1. PONSCalendar problem with BC era
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    <p>Greetings,</p> <p>Recently I faced a big problem (as it seems to me) with NSCalendar class.</p> <p>In my task I need to work with a large time periods starting from 4000BC to 2000AD (Gregorian calendar). In some place I was forced to increment some NSDate by 100 year interval. When incrementing the years in AD timeline (0->...) everything worked fine, but when I tried the same thing with BC i was a little confused.</p> <p>The problem is, when you try to add 100 years to 3000BC [edited] year, you get 3100BC [edited] no matter what... Personally i found it strange and illogical. The right result should be 2900BC.</p> <p>Here is the code sample for you to see this "not right" behavior:</p> <pre><code>NSCalendar *gregorian = [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] autorelease]; // initing NSDateComponents *comps = [[[NSDateComponents alloc] init] autorelease]; [comps setYear:-1000]; NSDate *date = [gregorian dateFromComponents:comps]; // math NSDateComponents *deltaComps = [[[NSDateComponents alloc] init] autorelease]; [deltaComps setYear:100]; date = [gregorian dateByAddingComponents:deltaComps toDate:date options:0]; // output NSString *dateFormat = @"yyyy GG"; NSDateFormatter *formatter = [[NSDateFormatter alloc] init]; [formatter setDateFormat:dateFormat]; NSLog(@"%@", [formatter stringFromDate:date]); </code></pre> <p>What can you say about this behavior? Is this how it should work or is this a bug? I'm confused :S.</p> <p>BTW.: the method [NSCalendar components:fromDate:toDate:options:] doesn't allow us to calculate the difference between years in BC era... additional 'WHY?' in this Pandora's box.</p> <p>P.S.: I was digging through official documentation and other resources but found nothing regarding this problem (or maybe it's intended to work so and I'm an idiot?).</p>
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    1. USGregoryM
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    1. CO3000AD + 100AD = 3100AD. This is basic arithmetic. From your description, the math is correct. Within your code, you want to add -1000 to -100 to get 1100BC, I suspect, but since you haven't shown us the output from your code, we don't know how it's misbehaving.
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      1. USJonathan Grynspan
    2. CO“… when you try to add 100 years to 3000AD year, you get 3100AD no matter what... Personally i found it strange and illogical. The right result should be 2900BC” Did you mean to say “BC” throughout that paragraph? Otherwise, it doesn't make sense: AD 3000 + 100 = AD 3100; that is the correct result.
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      1. USPeter Hosey
    3. COJonathan: sorry, i made a mistake, it's not an AD, it's BC.
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      1. USGregoryM
 

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