Issue with calculating difference between two dates - iphone

Question

I need to calculate difference between two days in minutes.
NSDate *now = [[NSDate alloc] init];
NSDateFormatter *outputFormatter = [[NSDateFormatter alloc] init];
[outputFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:#"en_US_POSIX"]];
[outputFormatter setDateFormat:#"dd/MM/yyyy hh:mm:ss a"];
NSString* dateStringFromDatabase = #"01/01/1900 11:00:00 AM";
NSDate* dateFromString = [outputFormatter dateFromString:dateStringFromDatabase];
NSString* a = [outputFormatter stringFromDate:now];
NSDate* b = [outputFormatter dateFromString:a];
NSCalendar *gregorian = [[NSCalendar alloc]initWithCalendarIdentifier:NSGregorianCalendar];
unsigned int unitFlags = NSHourCalendarUnit | NSMinuteCalendarUnit | NSDayCalendarUnit | NSMonthCalendarUnit;
NSDateComponents *components = [gregorian components:unitFlags fromDate:dateFromString
toDate:b options:0];
int hours = [components hour];
int minutes = [components minute];
self.lblResult.text = [NSString stringWithFormat:#"%i:%i", hours, minutes];
But I have the following issues:
For current hours I get:
2012-10-21 07:37:09 +0000 // wrong it's two hours late
When I try to cast #"01/01/1900 11:00:00 AM" to NSDate I get
1900-01-01 10:00:00 +0000 // also two hours late

Answer 1

Try This..................
if you have date in String then convert it into date using #"dd/MM/yyyy hh:mm:ss a"
NSDate *startDate = ...;
NSDate *endDate = ...;
Now Date comparison
// Date Comparision
NSCalendar *gregorian = [[NSCalendar alloc]initWithCalendarIdentifier:NSGregorianCalendar];
unsigned int unitFlags = NSHourCalendarUnit | NSMinuteCalendarUnit | NSDayCalendarUnit | NSMonthCalendarUnit;
NSDateComponents *components = [gregorian components:unitFlags fromDate:LastDate
toDate:CuurentDate options:0];
Getting the difference between two dates
int months = [components month];
int days = [components day];
int hours = [components hour];
int minutes = [components minute];

Answer 2

You need to set the -dateStyle rather than the time style, as there is also a date contained in that string.
Edit---
You now need to change the -dateFormat to dd/MM/yyyy HH:mm:ss a

Answer 3

I hope this helps
NSString *dtString = #"1900-01-01T11:00:00";
dtString = [dtString stringByReplacingOccurrencesOfString:#"T" withString:#" "];
NSDate *today = [NSDate date];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:#"YYYY-MM-dd HH:mm:ss"];
NSString *currentTime = [dateFormatter stringFromDate:today];
NSDate *toTimeDate = [dateFormatter dateFromString:dtString];
NSString *toTime = [dateFormatter stringFromDate:toTimeDate];