I'd like to convert an Int
in Swift to a String
with leading zeros. For example consider this code:
for myInt in 1 ... 3 {
print("\(myInt)")
}
Currently the result of it is:
1
2
3
But I want it to be:
01
02
03
Is there a clean way of doing this within the Swift standard libraries?
This question is related to
string
swift
int
type-conversion
Xcode 9.0.1, swift 4.0
Data
import Foundation
let array = [0,1,2,3,4,5,6,7,8]
Solution 1
extension Int {
func getString(prefix: Int) -> String {
return "\(prefix)\(self)"
}
func getString(prefix: String) -> String {
return "\(prefix)\(self)"
}
}
for item in array {
print(item.getString(prefix: 0))
}
for item in array {
print(item.getString(prefix: "0x"))
}
Solution 2
for item in array {
print(String(repeatElement("0", count: 2)) + "\(item)")
}
Solution 3
extension String {
func repeate(count: Int, string: String? = nil) -> String {
if count > 1 {
let repeatedString = string ?? self
return repeatedString + repeate(count: count-1, string: repeatedString)
}
return self
}
}
for item in array {
print("0".repeate(count: 3) + "\(item)")
}
Swift 4* and above you can try this also:
func leftPadding(valueString: String, toLength: Int, withPad: String = " ") -> String {
guard toLength > valueString.count else { return valueString }
let padding = String(repeating: withPad, count: toLength - valueString.count)
return padding + valueString
}
call the function:
leftPadding(valueString: "12", toLength: 5, withPad: "0")
Output: "00012"
The other answers are good if you are dealing only with numbers using the format string, but this is good when you may have strings that need to be padded (although admittedly a little diffent than the question asked, seems similar in spirit). Also, be careful if the string is longer than the pad.
let str = "a str"
let padAmount = max(10, str.count)
String(repeatElement("-", count: padAmount - str.count)) + str
Output "-----a str"
With Swift 5, you may choose one of the three examples shown below in order to solve your problem.
String
's init(format:_:)
initializerFoundation
provides Swift String
a init(format:_:)
initializer. init(format:_:)
has the following declaration:
init(format: String, _ arguments: CVarArg...)
Returns a
String
object initialized by using a given format string as a template into which the remaining argument values are substituted.
The following Playground code shows how to create a String
formatted from Int
with at least two integer digits by using init(format:_:)
:
import Foundation
let string0 = String(format: "%02d", 0) // returns "00"
let string1 = String(format: "%02d", 1) // returns "01"
let string2 = String(format: "%02d", 10) // returns "10"
let string3 = String(format: "%02d", 100) // returns "100"
String
's init(format:arguments:)
initializerFoundation
provides Swift String
a init(format:arguments:)
initializer. init(format:arguments:)
has the following declaration:
init(format: String, arguments: [CVarArg])
Returns a
String
object initialized by using a given format string as a template into which the remaining argument values are substituted according to the user’s default locale.
The following Playground code shows how to create a String
formatted from Int
with at least two integer digits by using init(format:arguments:)
:
import Foundation
let string0 = String(format: "%02d", arguments: [0]) // returns "00"
let string1 = String(format: "%02d", arguments: [1]) // returns "01"
let string2 = String(format: "%02d", arguments: [10]) // returns "10"
let string3 = String(format: "%02d", arguments: [100]) // returns "100"
NumberFormatter
Foundation provides NumberFormatter
. Apple states about it:
Instances of
NSNumberFormatter
format the textual representation of cells that containNSNumber
objects and convert textual representations of numeric values intoNSNumber
objects. The representation encompasses integers, floats, and doubles; floats and doubles can be formatted to a specified decimal position.
The following Playground code shows how to create a NumberFormatter
that returns String?
from a Int
with at least two integer digits:
import Foundation
let formatter = NumberFormatter()
formatter.minimumIntegerDigits = 2
let optionalString0 = formatter.string(from: 0) // returns Optional("00")
let optionalString1 = formatter.string(from: 1) // returns Optional("01")
let optionalString2 = formatter.string(from: 10) // returns Optional("10")
let optionalString3 = formatter.string(from: 100) // returns Optional("100")
Swift 3.0+
Left padding String
extension similar to padding(toLength:withPad:startingAt:)
in Foundation
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
}
}
Usage:
let s = String(123)
s.leftPadding(toLength: 8, withPad: "0") // "00000123"
Using Swift 5’s fancy new extendible interpolation:
extension DefaultStringInterpolation {
mutating func appendInterpolation(pad value: Int, toWidth width: Int, using paddingCharacter: Character = "0") {
appendInterpolation(String(format: "%\(paddingCharacter)\(width)d", value))
}
}
print("I ate \(pad: pieCount, toWidth: 3, using: "0") pies") // => `I ate 003 pies`
in Xcode 8.3.2, iOS 10.3 Thats is good to now
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
For left padding add a string extension like this:
Swift 2.0 +
extension String {
func padLeft (totalWidth: Int, with: String) -> String {
let toPad = totalWidth - self.characters.count
if toPad < 1 { return self }
return "".stringByPaddingToLength(toPad, withString: with, startingAtIndex: 0) + self
}
}
Swift 3.0 +
extension String {
func padLeft (totalWidth: Int, with: String) -> String {
let toPad = totalWidth - self.characters.count
if toPad < 1 { return self }
return "".padding(toLength: toPad, withPad: with, startingAt: 0) + self
}
}
Using this method:
for myInt in 1...3 {
print("\(myInt)".padLeft(totalWidth: 2, with: "0"))
}
Unlike the other answers that use a formatter, you can also just add an "0" text in front of each number inside of the loop, like this:
for myInt in 1...3 {
println("0" + "\(myInt)")
}
But formatter is often better when you have to add suppose a designated amount of 0s for each seperate number. If you only need to add one 0, though, then it's really just your pick.
@imanuo answers is already great, but if you are working with an application full of number, you can consider an extension like this:
extension String {
init(withInt int: Int, leadingZeros: Int = 2) {
self.init(format: "%0\(leadingZeros)d", int)
}
func leadingZeros(_ zeros: Int) -> String {
if let int = Int(self) {
return String(withInt: int, leadingZeros: zeros)
}
print("Warning: \(self) is not an Int")
return ""
}
}
In this way you can call wherever:
String(withInt: 3)
// prints 03
String(withInt: 23, leadingZeros: 4)
// prints 0023
"42".leadingZeros(2)
// prints 42
"54".leadingZeros(3)
// prints 054
Source: Stackoverflow.com