Question

how to calculate Mid night time intervals in iphone development?

i am working on stock market app, and i need to calculate a timeinterval after market closed.

suppose stock market is closed at 6:30 pm after that i need to time interval till 12:00

Answer 1

Yes, You really should provide more info about your input data.
Because if you have two NSDate values containing full date and time info you need nothing more than timeIntervalSinceDate:

    NSDateFormatter * dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"MM.dd.yyyy hh:mm a"];    
    NSDate * date1 = [dateFormatter dateFromString:@"01.11.2011 06:30 PM"];
    NSDate * date2 = [dateFormatter dateFromString:@"01.12.2011 12:00 PM"];
    NSTimeInterval interval = [date2 timeIntervalSinceDate:date1];

You’ll get 63000 s = 17.5 h

But it looks like you have times without date information. In this case you’ll get wrong negative value:

[dateFormatter setDateFormat:@"hh:mm a"];
NSDate * date1 = [dateFormatter dateFromString:@"06:30 PM"];
NSDate * date2 = [dateFormatter dateFromString:@"12:00 PM"];
NSTimeInterval interval = [date2 timeIntervalSinceDate:date1];

result is -23400 s = -6.5 h

So in this case you should correct the result, because you know second date is after midnight:

NSTimeInterval rightInterval = 24*3600 + [date2 timeIntervalSinceDate:date1];