如何在NSDecimalNumber中存储1.66 [英] How to store 1.66 in NSDecimalNumber

问题描述

我知道float或double不能很好地存储货币和数量等十进制数字.我正在尝试使用NSDecimalNumber代替.这是我在Swift操场上的代码.

I know float or double are not good for storing decimal number like money and quantity. I'm trying to use NSDecimalNumber instead. Here is my code in Swift playground.

let number:NSDecimalNumber = 1.66
let text:String = String(describing: number)
NSLog(text)

控制台输出为1.6599999999999995904

The console output is 1.6599999999999995904

如何将十进制数字1.66的确切值存储在变量中?

How can I store the exact value of the decimal number 1.66 in a variable?

推荐答案

在

let number:NSDecimalNumber = 1.66

右侧是一个浮点数，不能表示 值"1.66"正好.一种选择是创建十进制数 从字符串:

the right-hand side is a floating point number which cannot represent the value "1.66" exactly. One option is to create the decimal number from a string:

let number = NSDecimalNumber(string: "1.66")
print(number) // 1.66

另一种选择是使用算术:

Another option is to use arithmetic:

let number = NSDecimalNumber(value: 166).dividing(by: 100)
print(number) // 1.66

在Swift 3中，您可以考虑使用覆盖值类型" Decimal，例如

With Swift 3 you may consider to use the "overlay value type" Decimal instead, e.g.

let num = Decimal(166)/Decimal(100)
print(num) // 1.66

另一个选择:

let num = Decimal(sign: .plus, exponent: -2, significand: 166)
print(num) // 1.66

附录:

Swift论坛中的相关讨论:

Related discussions in the Swift forum:

• 通过文字精确的NSDecimalNumber
• ExpressibleByFractionLiteral

• Exact NSDecimalNumber via literal
• ExpressibleByFractionLiteral

相关的错误报告:

• SR-3317 十进制字面量的文字协议应支持精确的十进制精度，应作为
的副本关闭
• SR-920 重新设计用于文字可转换类型的内置编译器协议.

• SR-3317 Literal protocol for decimal literals should support precise decimal accuracy, closed as a duplicate of
• SR-920 Re-design builtin compiler protocols for literal convertible types.

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