谁能告诉我如何在Swift中舍入一个双数值到x位小数点后数位?
我有:
var totalWorkTimeInHours = (totalWorkTime/60/60)
totalWorkTime是一个NSTimeInterval (double),单位为秒。
totalWorkTimeInHours会给我小时数,但它给我的时间量是如此长的精确数字,例如1.543240952039......
当我打印totalWorkTimeInHours时,我如何将其四舍五入到1.543 ?
谁能告诉我如何在Swift中舍入一个双数值到x位小数点后数位?
我有:
var totalWorkTimeInHours = (totalWorkTime/60/60)
totalWorkTime是一个NSTimeInterval (double),单位为秒。
totalWorkTimeInHours会给我小时数,但它给我的时间量是如此长的精确数字,例如1.543240952039......
当我打印totalWorkTimeInHours时,我如何将其四舍五入到1.543 ?
当前回答
:
Using String(format:): Typecast Double to String with %.3f format specifier and then back to Double Double(String(format: "%.3f", 10.123546789))! Or extend Double to handle N-Decimal places: extension Double { func rounded(toDecimalPlaces n: Int) -> Double { return Double(String(format: "%.\(n)f", self))! } } By calculation multiply with 10^3, round it and then divide by 10^3... (1000 * 10.123546789).rounded()/1000 Or extend Double to handle N-Decimal places: extension Double { func rounded(toDecimalPlaces n: Int) -> Double { let multiplier = pow(10, Double(n)) return (multiplier * self).rounded()/multiplier } }
其他回答
不是斯威夫特,但我相信你明白我的意思。
pow10np = pow(10,num_places);
val = round(val*pow10np) / pow10np;
//find the distance between two points
let coordinateSource = CLLocation(latitude: 30.7717625, longitude:76.5741449 )
let coordinateDestination = CLLocation(latitude: 29.9810859, longitude: 76.5663599)
let distanceInMeters = coordinateSource.distance(from: coordinateDestination)
let valueInKms = distanceInMeters/1000
let preciseValueUptoThreeDigit = Double(round(1000*valueInKms)/1000)
self.lblTotalDistance.text = "Distance is : \(preciseValueUptoThreeDigit) kms"
这是一个完整的代码
Swift 3.0/4.0/5.0, Xcode 9.0 GM/9.2及以上
let doubleValue : Double = 123.32565254455
self.lblValue.text = String(format:"%.f", doubleValue)
print(self.lblValue.text)
输出- 123
let doubleValue : Double = 123.32565254455
self.lblValue_1.text = String(format:"%.1f", doubleValue)
print(self.lblValue_1.text)
输出- 123.3
let doubleValue : Double = 123.32565254455
self.lblValue_2.text = String(format:"%.2f", doubleValue)
print(self.lblValue_2.text)
输出- 123.33
let doubleValue : Double = 123.32565254455
self.lblValue_3.text = String(format:"%.3f", doubleValue)
print(self.lblValue_3.text)
输出- 123.326
一个方便的方法是使用Double类型的扩展
extension Double {
var roundTo2f: Double {return Double(round(100 *self)/100) }
var roundTo3f: Double {return Double(round(1000*self)/1000) }
}
用法:
let regularPie: Double = 3.14159
var smallerPie: Double = regularPie.roundTo3f // results 3.142
var smallestPie: Double = regularPie.roundTo2f // results 3.14
Swift 2扩展
一个更通用的解决方案是以下扩展,适用于Swift 2和iOS 9:
extension Double {
/// Rounds the double to decimal places value
func roundToPlaces(places:Int) -> Double {
let divisor = pow(10.0, Double(places))
return round(self * divisor) / divisor
}
}
Swift 3扩展
在Swift 3中,round被圆润取代:
extension Double {
/// Rounds the double to decimal places value
func rounded(toPlaces places:Int) -> Double {
let divisor = pow(10.0, Double(places))
return (self * divisor).rounded() / divisor
}
}
返回Double四舍五入到小数点后4位的示例:
let x = Double(0.123456789).roundToPlaces(4) // x becomes 0.1235 under Swift 2
let x = Double(0.123456789).rounded(toPlaces: 4) // Swift 3 version