How calculate time from current time?

I have design an application in which i am have three text field in wh开发者_开发知识库ich i am giving my time like as 10:10 PM. Now problem is that i want to calculate time difference between current time and entered time. How calculate time?

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Depending what you mean by "entered time" you will most likely need to look at NSDateFormatter and parse the entered time into a usable form, then get a date using NSDate (i.e. NSDate * now = [NSDate date];) and do whatever math you need using the methods available in `NSDate'.

If you are just determining the difference between entered date and now this method would suit you:

- (NSTimeInterval)timeIntervalSinceNow

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you can get the difference in seconds using time intervals (e.g. that of the NSDate and CFAbsoluteTimeGetCurrent).