This blogpost will focus on the setDateFormat: method of NSDateFormatter which allow us to define the date format of the textual representation of the date and time in iOS/Cocoa. Here’s a summary of the specifiers used in the date format string.
The most commonly used date format specifiers are (keep in mind that they are case sensitive):
- y = year
- Q = quarter
- M = month
- w = week of year
- W = week of month
- d = day of the month
- D = day of year
- E = day of week
- a = period (AM or PM)
- h = hour (1-12)
- H = hour (0-23)
- m = minute
- s = second
In general, the number of characters in a specifier determine the size of date field. Let’s use an example to illustrate date formatting.
eg. Input date = 2011-05-01 Sunday
1-character = 1-digit/character number or word (if number/word can’t be 1 character long then abbreviation or fullname is displayed).
[dateFormatter setDateFormat:@"E, d M y"]; // Output: Sun, 1 5 2011
2-character = 2-digit/character number or word (if number/word can’t be 2 character long then abbreviation is displayed).
[dateFormatter setDateFormat:@"EE, dd MM yy"]; // Output: Sun, 01 05 11
3-character = 3-digit/character number or word, or abbreviation (generally).
[dateFormatter setDateFormat:@"EEE, ddd MMM yyy"]; // Output: Sun, 001 May 2011
4-character = full name (generally).
[dateFormatter setDateFormat:@"EEEE, dddd MMMM yyyy"]; // Output: Sunday, 0001 May 2011
Here’s the weird part though, if you specify 5 E’s, you get an rather unexpected output. You would think that the output date field would be longer than 1 character:
[dateFormatter setDateFormat:@"EEEEE, ddddd MMMMM yyyyy"]; // Output: S, 00001 M 2011
For date formatting, the following reference table has been very useful: