我想将Swift中的Int转换为带前导零的字符串。例如,考虑以下代码:

for myInt in 1 ... 3 {
    print("\(myInt)")
}

目前的结果是:

1
2
3

但我希望它是:

01
02
03

在Swift标准库中是否有一种干净的方式来做到这一点?


当前回答

对于左填充,添加一个字符串扩展,如下所示:

Swift 5.0 +

extension String {

    func padLeft(totalWidth: Int, with byString: String) -> String {
        let toPad = totalWidth - self.count
        if toPad < 1 {
            return self
        }
    
        return "".padding(toLength: toPad, withPad: byString, startingAt: 0) + self
    }
}

使用这种方法:

for myInt in 1...3 {
    print("\(myInt)".padLeft(totalWidth: 2, with: "0"))
}

其他回答

Swift 3.0 +

左填充字符串扩展,类似于填充(toLength:withPad:startingAt:)在基础

extension String {
    func leftPadding(toLength: Int, withPad: String = " ") -> String {

        guard toLength > self.characters.count else { return self }

        let padding = String(repeating: withPad, count: toLength - self.characters.count)
        return padding + self
    }
}

用法:

let s = String(123)
s.leftPadding(toLength: 8, withPad: "0") // "00000123"

对于左填充,添加一个字符串扩展,如下所示:

Swift 5.0 +

extension String {

    func padLeft(totalWidth: Int, with byString: String) -> String {
        let toPad = totalWidth - self.count
        if toPad < 1 {
            return self
        }
    
        return "".padding(toLength: toPad, withPad: byString, startingAt: 0) + self
    }
}

使用这种方法:

for myInt in 1...3 {
    print("\(myInt)".padLeft(totalWidth: 2, with: "0"))
}

下面的代码生成了一个前面填充为0的3位字符串:

import Foundation

var randomInt = Int.random(in: 0..<1000)
var str = String(randomInt)
var paddingZero = String(repeating: "0", count: 3 - str.count)

print(str, str.count, paddingZero + str)

输出:

5 1 005
88 2 088
647 3 647

在Xcode 8.3.2, iOS 10.3 这对现在来说很好

Sample1:

let dayMoveRaw = 5 
let dayMove = String(format: "%02d", arguments: [dayMoveRaw])
print(dayMove) // 05

Sample2:

let dayMoveRaw = 55 
let dayMove = String(format: "%02d", arguments: [dayMoveRaw])
print(dayMove) // 55

与其他使用格式化器的答案不同,你也可以在循环内的每个数字前面添加一个“0”文本,就像这样:

for myInt in 1...3 {
    println("0" + "\(myInt)")
}

但是,当您必须为每个单独的数字添加指定数量的0时,formatter通常更好。如果你只需要加一个0,那么它就是你的选择。