在 iphone sdk 中使用 NSNumberFormatter 和 NSDecimalNumberHandler
作为我正在做的格式化非常大、精确的数字的快速测试：
(number is a synthesized NSDecimalNumber...) number = [[NSDecimalNumber alloc] initWithDecimal:[[NSDecimalNumber numberWithDouble:420000008698643507200000.0F] decimalValue]]; DLog(@"unformatted: %@", [number stringValue]);
这给了我：“未格式化：420000008698643507200000”
，但是当我尝试通过 NSNumberFormatter 格式化它时，它非常不对......舍入方式或其他...
numFormatter = [[NSNumberFormatter alloc] init]; [numFormatter setNumberStyle:kCFNumberFormatterDecimalStyle]; [numFormatter setRoundingMode:kCFNumberFormatterRoundDown]; [numFormatter setMaximum:nil]; DLog(@"formatted: %@", [numFormatter stringFromNumber:number]);
给我：“formatted: 420,000,008,698,644,000,000,000”
我希望有一些我没有看到的秘密 NSNumberFormatter 魔法属性，但我尝试了 setUsesSignificantDigits 并且setMaximumSignificantDigits，但这似乎不起作用。
有人有主意吗？ 非常感谢！
as a quick test of formatting very large, precise numbers i'm doing:
(number is a synthesized NSDecimalNumber...) number = [[NSDecimalNumber alloc] initWithDecimal:[[NSDecimalNumber numberWithDouble:420000008698643507200000.0F] decimalValue]]; DLog(@"unformatted: %@", [number stringValue]);
which gives me: "unformatted: 420000008698643507200000"
but when i try to format it via NSNumberFormatter, it's quite off... rounding way up or something...
numFormatter = [[NSNumberFormatter alloc] init]; [numFormatter setNumberStyle:kCFNumberFormatterDecimalStyle]; [numFormatter setRoundingMode:kCFNumberFormatterRoundDown]; [numFormatter setMaximum:nil]; DLog(@"formatted: %@", [numFormatter stringFromNumber:number]);
gives me: "formatted: 420,000,008,698,644,000,000,000"
i'm hoping there's some secret NSNumberFormatter magic property that i'm not seeing, but I tried setUsesSignificantDigits and setMaximumSignificantDigits, but that didn't seem to work.
anyone have any ideas? thanks a bunch!
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您的精度损失来自于
NSNumberFormatter将数字转换为双精度的事实。您是否考虑过使用
NSDecimalNumber的descriptionWithLocale:方法？ 作为起点，您只需传入[NSLocale currentLocale]作为参数即可。 然后，您可以开始通过 NSLocaleDecimalSeparator 和 NSLocaleGroupingSeparator 来使用区域设置配置。Your loss of precision comes from the fact that
NSNumberFormatterconverts the number to a double.Have you considered using
NSDecimalNumber's descriptionWithLocale:method? As a starting point you could just pass in[NSLocale currentLocale]as a param. Then you can start playing with the locale configuration viaNSLocaleDecimalSeparatorandNSLocaleGroupingSeparator.