Date with month name date, year in objective-c - objective-c

Question

I have a date string formatted as "September 10, 2013". How can I convert this representation into a format such as "yyyy/mm/dd".
NSString *strDate = #"September 10, 2013";
NSDateFormatter *df = [[NSDateFormatter alloc] init];
[df dateFromString:strDate];
NSDate *date = [df dateFromString:strDate];
[df setDateFormat:#"yyyy/mm/dd"];
NSString* temp = [[NSString alloc] init];
temp = [df stringFromDate:date];
NSLog(#"date i required %#", temp);
temp object is null here.
Thanks in advance.

Answer 1

Let's rework your original code, and discuss it as well:
NSString *strDate = #"September 10, 2013";
NSDateFormatter *df = [[NSDateFormatter alloc] init];
For the input you're attempting to parse, you've got to provide a format string for your date formatter. If you don't, the date formatter is going to use defaults that are determined by the settings in your Date & Time control panel. Not only do these settings vary from locale to locale, they're subject to whatever changes the user may have effected. Another way of putting it is that they might not match the format of the date string you're attempting to convert.
You also don't want to rely on predefined styles such as NSDateFormatterShortStyle, NSDateFormatterMediumStyle or NSDateFormatterLongStyle. They're meant for date display (if you're willing to accept the Date & Time control panel settings), not for parsing.
There's a document you should consult, which is Unicode Technical Standard #35. Look in the table labeled "Date Field Symbol Table." Based on the information presented there (and your input), you'd set up your date converter to parse with a format string like this one:
[df setDateFormat:#"MMMM dd, yyyy"];
Now you can use your date formatter to parse your date string, and it'll work:
NSDate *date = [df dateFromString:strDate];
From this point onward, you're looking pretty good (though I've removed a superfluous line or two throughout all of this):
[df setDateFormat:#"yyyy/MM/dd"];
NSString *temp = [df stringFromDate:date];
NSLog(#"date i required %#", temp);
Best wishes to you in your endeavors.

Answer 2

You can use the NSDateFormatterclass -- look at the stringFromDate and dateFromString methods.
UPDATE: you have a couple of problems -- first, you need to tell the formatter what the initial format should be. Second, you have a format problem with the second format string -- 'm' is minutes, 'M' is months. You should review the documentation here. Here is an example:
NSString *strDate = #"September 10, 2013";
NSDateFormatter *df = [[NSDateFormatter alloc] init];
[df setDateStyle:NSDateFormatterLongStyle];
[df dateFromString:strDate];
NSDate *dat = [df dateFromString:strDate];
[df setDateFormat:#"yyyy/MM/dd"];
NSString* t = [df stringFromDate:dat];
NSLog(#"date i required %#", t);