Swift language bug in DateFormatter? [duplicate] - swift

Question

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Closed 5 years ago.
I was testing an app that has an UITextField where users enter a date, so I take the entered string and use a DateFormatter to generate a Date object.
The problem first occurred when I tried converting the string "10/15/2017" which returned a nil value. So I create a code to generate string from "01/01/2000" to "12/31/2020" and I realized that the problem is occurring in all years around October or November of each year.
I created a code to print all dates that return a nil value:
import UIKit
let dateFormatter = DateFormatter()
dateFormatter.dateStyle = .short
dateFormatter.locale = Locale(identifier: "en_US")
for day in 1...30 { // Generate the days
for month in 1...12 { // Generate the months
for year in 2000...2020 {
if month == 2, day > 28 { // Check if month is february
continue
}
str = "\(String(format: "%02d", month))/\(String(format: "%02d", day))/\(String(format: "%02d", year))"
let date = dateFormatter.date(from: str)
if date == nil {
print("\(str)")
}
}
}
}
I also tried changing the dateFormat, or even the locale properties and I'm also getting nil for some entries.
dateFormatter.dateFormat = "MM/dd/yyyy"
This snippet of code prints the following:
11/02/2004
11/03/2002
11/05/2006
10/08/2000
10/14/2001
10/14/2007
10/15/2017
10/16/2005
10/16/2011
10/16/2016
10/17/2010
10/18/2009
10/18/2015
10/18/2020
10/19/2003
10/19/2008
10/19/2014
10/20/2013
10/20/2019
10/21/2012
10/21/2018
I'm using Xcode 8.3.3 and Swift 3. Is that a bug with Swift/Xcode or I'm doing something wrong?

Answer 1

It's most likely the Brazil-Fall-Syndrome
The daylight saving changes in Brazil occur at midnight. In fall, when the clock is set forward, there is no 12:00 am / 0:00 so the date is nil.
Set the time zone to a country where daylight saving changes don't occur at midnight or set the hour to noon