如何使用 NSDecimalNumber? [英] How to use NSDecimalNumber?

问题描述

我正在构建一个需要对金钱进行计算的应用.

I'm building a app that needs to perform calculations on money.

我想知道如何正确使用 NSDecimalNumber，尤其是如何从整数、浮点数和双打?

I wonder how to properly use NSDecimalNumber, especially how to initialize it from integers, floats & doubles?

我只发现使用 -decimalNumberWithString: 方法很容易.不鼓励使用 -initWith... 方法，因此只留下带有尾数的方法，但在我之前使用的 7 种语言中的任何一种中，我都不需要它，所以我不知道那里放了什么...

I only found it easy to use the -decimalNumberWithString: method. The -initWith... methods are discouraged so that only left the ones with mantissa, but never in any of 7 languages I used before did I need that so I don't know what put there...

推荐答案

Do NOT 使用 NSNumber 的 +numberWith... 方法创建 NSDecimalNumber 对象.它们被声明为返回 NSNumber 对象，并且不能保证作为 NSDecimalNumber 实例运行.

Do NOT use NSNumber's +numberWith... methods to create NSDecimalNumber objects. They are declared to return NSNumber objects and are not guaranteed to function as NSDecimalNumber instances.

这在 Bill 的 thread 中有解释Bumgarner，苹果公司的一名开发人员.我鼓励您针对此行为提交错误，参考错误 rdar://6487304.

This is explained in this thread by Bill Bumgarner, a developer at Apple. I would encourage you to file a bug against this behavior, referencing bug rdar://6487304.

作为替代，这些是用于创建 NSDecimalNumber 的所有适当方法:

As an alternative these are all of the appropriate methods to use to create an NSDecimalNumber:

+ (NSDecimalNumber *)decimalNumberWithMantissa:(unsigned long long)mantissa
                     exponent:(short)exponent isNegative:(BOOL)flag;
+ (NSDecimalNumber *)decimalNumberWithDecimal:(NSDecimal)dcm;
+ (NSDecimalNumber *)decimalNumberWithString:(NSString *)numberValue;
+ (NSDecimalNumber *)decimalNumberWithString:(NSString *)numberValue locale:(id)locale;

+ (NSDecimalNumber *)zero;
+ (NSDecimalNumber *)one;
+ (NSDecimalNumber *)minimumDecimalNumber;
+ (NSDecimalNumber *)maximumDecimalNumber;
+ (NSDecimalNumber *)notANumber;

如果您只是想要 float 或 int 常量中的 NSDecimalNumber，请尝试以下操作:

If you simply want an NSDecimalNumber from a float or int constant try something like this:

NSDecimalNumber *dn = [NSDecimalNumber decimalNumberWithDecimal:
                             [[NSNumber numberWithFloat:2.75f] decimalValue];

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