下面是我以前如何将一个浮点数截断到小数点后两位
NSLog(@" %.02f %.02f %.02f", r, g, b);
我查了文档和电子书，但还没找到答案。谢谢!
当前回答
use
CGFloat
or
Float.roundTo(places:2)
其他回答
我目前为止最好的解决方案，以下是David的回答:
import Foundation
extension Int {
func format(f: String) -> String {
return String(format: "%\(f)d", self)
}
}
extension Double {
func format(f: String) -> String {
return String(format: "%\(f)f", self)
}
}
let someInt = 4, someIntFormat = "03"
println("The integer number \(someInt) formatted with \"\(someIntFormat)\" looks like \(someInt.format(someIntFormat))")
// The integer number 4 formatted with "03" looks like 004
let someDouble = 3.14159265359, someDoubleFormat = ".3"
println("The floating point number \(someDouble) formatted with \"\(someDoubleFormat)\" looks like \(someDouble.format(someDoubleFormat))")
// The floating point number 3.14159265359 formatted with ".3" looks like 3.142
我认为这是最类似swift的解决方案，将格式化操作直接绑定到数据类型上。很可能在某个地方有一个内置的格式化操作库，或者它很快就会发布。请记住，该语言仍处于测试阶段。
你仍然可以在Swift中使用NSLog，就像在Objective-C中一样，只是没有@符号。
NSLog("%.02f %.02f %.02f", r, g, b)
编辑:在与Swift合作一段时间后，我想添加这个变化
var r=1.2
var g=1.3
var b=1.4
NSLog("\(r) \(g) \(b)")
输出:
2014-12-07 21:00:42.128 MyApp[1626:60b] 1.2 1.3 1.4
import Foundation
extension CGFloat {
var string1: String {
return String(format: "%.1f", self)
}
var string2: String {
return String(format: "%.2f", self)
}
}
使用
let offset = CGPoint(1.23, 4.56)
print("offset: \(offset.x.string1) x \(offset.y.string1)")
// offset: 1.2 x 4.6
斯威夫特4
let string = String(format: "%.2f", locale: Locale.current, arguments: 15.123)
细节
Xcode 9.3, Swift 4.1 Xcode 10.2.1 (10E1001)
解决方案1
func round () -> Double
(5.2).rounded()
// 5.0
(5.5).rounded()
// 6.0
(-5.2).rounded()
// -5.0
(-5.5).rounded()
// -6.0
func圆润(_ rule: FloatingPointRoundingRule) -> Double
let x = 6.5
// Equivalent to the C 'round' function:
print(x.rounded(.toNearestOrAwayFromZero))
// Prints "7.0"
// Equivalent to the C 'trunc' function:
print(x.rounded(.towardZero))
// Prints "6.0"
// Equivalent to the C 'ceil' function:
print(x.rounded(.up))
// Prints "7.0"
// Equivalent to the C 'floor' function:
print(x.rounded(.down))
// Prints "6.0"
func round()
var x = 5.2
x.round()
// x == 5.0
var y = 5.5
y.round()
// y == 6.0
var z = -5.5
z.round()
// z == -6.0
func round(_ rule: FloatingPointRoundingRule)
// Equivalent to the C 'round' function:
var w = 6.5
w.round(.toNearestOrAwayFromZero)
// w == 7.0
// Equivalent to the C 'trunc' function:
var x = 6.5
x.round(.towardZero)
// x == 6.0
// Equivalent to the C 'ceil' function:
var y = 6.5
y.round(.up)
// y == 7.0
// Equivalent to the C 'floor' function:
var z = 6.5
z.round(.down)
// z == 6.0
解决方案2
extension Numeric {
private func _precision(number: NSNumber, formatter: NumberFormatter) -> Self? {
if let formatedNumString = formatter.string(from: number),
let formatedNum = formatter.number(from: formatedNumString) {
return formatedNum as? Self
}
return nil
}
private func toNSNumber() -> NSNumber? {
if let num = self as? NSNumber { return num }
guard let string = self as? String, let double = Double(string) else { return nil }
return NSNumber(value: double)
}
func precision(_ minimumFractionDigits: Int,
roundingMode: NumberFormatter.RoundingMode = NumberFormatter.RoundingMode.halfUp) -> Self? {
guard let number = toNSNumber() else { return nil }
let formatter = NumberFormatter()
formatter.minimumFractionDigits = minimumFractionDigits
formatter.roundingMode = roundingMode
return _precision(number: number, formatter: formatter)
}
func precision(with numberFormatter: NumberFormatter) -> String? {
guard let number = toNSNumber() else { return nil }
return numberFormatter.string(from: number)
}
}
使用
_ = 123.44.precision(2)
_ = 123.44.precision(3, roundingMode: .up)
let numberFormatter = NumberFormatter()
numberFormatter.minimumFractionDigits = 1
numberFormatter.groupingSeparator = " "
let num = 222.3333
_ = num.precision(2)
完整的样品
func option1<T: Numeric>(value: T, numerFormatter: NumberFormatter? = nil) {
print("Type: \(type(of: value))")
print("Original Value: \(value)")
let value1 = value.precision(2)
print("value1 = \(value1 != nil ? "\(value1!)" : "nil")")
let value2 = value.precision(5)
print("value2 = \(value2 != nil ? "\(value2!)" : "nil")")
if let value1 = value1, let value2 = value2 {
print("value1 + value2 = \(value1 + value2)")
}
print("")
}
func option2<T: Numeric>(value: T, numberFormatter: NumberFormatter) {
print("Type: \(type(of: value))")
print("Original Value: \(value)")
let value1 = value.precision(with: numberFormatter)
print("formated value = \(value1 != nil ? "\(value1!)" : "nil")\n")
}
func test(with double: Double) {
print("===========================\nTest with: \(double)\n")
let float = Float(double)
let float32 = Float32(double)
let float64 = Float64(double)
let float80 = Float80(double)
let cgfloat = CGFloat(double)
// Exapmle 1
print("-- Option1\n")
option1(value: double)
option1(value: float)
option1(value: float32)
option1(value: float64)
option1(value: float80)
option1(value: cgfloat)
// Exapmle 2
let numberFormatter = NumberFormatter()
numberFormatter.formatterBehavior = .behavior10_4
numberFormatter.minimumIntegerDigits = 1
numberFormatter.minimumFractionDigits = 4
numberFormatter.maximumFractionDigits = 9
numberFormatter.usesGroupingSeparator = true
numberFormatter.groupingSeparator = " "
numberFormatter.groupingSize = 3
print("-- Option 2\n")
option2(value: double, numberFormatter: numberFormatter)
option2(value: float, numberFormatter: numberFormatter)
option2(value: float32, numberFormatter: numberFormatter)
option2(value: float64, numberFormatter: numberFormatter)
option2(value: float80, numberFormatter: numberFormatter)
option2(value: cgfloat, numberFormatter: numberFormatter)
}
test(with: 123.22)
test(with: 1234567890987654321.0987654321)
输出
===========================
Test with: 123.22
-- Option1
Type: Double
Original Value: 123.22
value1 = 123.22
value2 = 123.22
value1 + value2 = 246.44
Type: Float
Original Value: 123.22
value1 = nil
value2 = nil
Type: Float
Original Value: 123.22
value1 = nil
value2 = nil
Type: Double
Original Value: 123.22
value1 = 123.22
value2 = 123.22
value1 + value2 = 246.44
Type: Float80
Original Value: 123.21999999999999886
value1 = nil
value2 = nil
Type: CGFloat
Original Value: 123.22
value1 = 123.22
value2 = 123.22
value1 + value2 = 246.44
-- Option 2
Type: Double
Original Value: 123.22
formatted value = 123.2200
Type: Float
Original Value: 123.22
formatted value = 123.220001221
Type: Float
Original Value: 123.22
formatted value = 123.220001221
Type: Double
Original Value: 123.22
formatted value = 123.2200
Type: Float80
Original Value: 123.21999999999999886
formatted value = nil
Type: CGFloat
Original Value: 123.22
formatted value = 123.2200
===========================
Test with: 1.2345678909876544e+18
-- Option1
Type: Double
Original Value: 1.2345678909876544e+18
value1 = 1.23456789098765e+18
value2 = 1.23456789098765e+18
value1 + value2 = 2.4691357819753e+18
Type: Float
Original Value: 1.234568e+18
value1 = nil
value2 = nil
Type: Float
Original Value: 1.234568e+18
value1 = nil
value2 = nil
Type: Double
Original Value: 1.2345678909876544e+18
value1 = 1.23456789098765e+18
value2 = 1.23456789098765e+18
value1 + value2 = 2.4691357819753e+18
Type: Float80
Original Value: 1234567890987654400.0
value1 = nil
value2 = nil
Type: CGFloat
Original Value: 1.2345678909876544e+18
value1 = 1.23456789098765e+18
value2 = 1.23456789098765e+18
value1 + value2 = 2.4691357819753e+18
-- Option 2
Type: Double
Original Value: 1.2345678909876544e+18
formatted value = 1 234 567 890 987 650 000.0000
Type: Float
Original Value: 1.234568e+18
formatted value = 1 234 567 939 550 610 000.0000
Type: Float
Original Value: 1.234568e+18
formatted value = 1 234 567 939 550 610 000.0000
Type: Double
Original Value: 1.2345678909876544e+18
formatted value = 1 234 567 890 987 650 000.0000
Type: Float80
Original Value: 1234567890987654400.0
formatted value = nil
Type: CGFloat
Original Value: 1.2345678909876544e+18
formatted value = 1 234 567 890 987 650 000.0000
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