How to convert an NSDate into Unix timestamp? I've read many posts which do开发者_Go百科 the reverse. But I'm not finding anything related to my question.

I believe this is the NSDate's selector you're looking for:

- (NSTimeInterval)timeIntervalSince1970

A Unix timestamp is the number of seconds since 00:00:00 UTC January 1, 1970. It's represented by the type time_t, which is usually a signed 32-bit integer type (long or int).

iOS provides -(NSTimeInterval)timeIntervalSince1970 for NSDate objects which returns the number of seconds since 00:00:00 GMT January 1, 1970. NSTimeInterval is a double floating point type so you get the seconds and fractions of a second.

Since they both have the same reference (midnight 1Jan1970 UTC) and are both in seconds the conversion is easy, convert the NSTimeInterval to a time_t, rounding or truncating depending on your needs:

time_t unixTime = (time_t) [[NSDate date] timeIntervalSince1970];

You can create a unix timestamp date from a date this way:

NSTimeInterval timestamp = [[NSDate date] timeIntervalSince1970];

- (void)GetCurrentTimeStamp
    {
        NSDateFormatter *objDateformat = [[NSDateFormatter alloc] init];
        [objDateformat setDateFormat:@"yyyy-MM-dd"];
        NSString    *strTime = [objDateformat stringFromDate:[NSDate date]];
        NSString    *strUTCTime = [self GetUTCDateTimeFromLocalTime:strTime];//You can pass your date but be carefull about your date format of NSDateFormatter.
        NSDate *objUTCDate  = [objDateformat dateFromString:strUTCTime];
        long long milliseconds = (long long)([objUTCDate timeIntervalSince1970] * 1000.0);

        NSString *strTimeStamp = [Nsstring stringwithformat:@"%lld",milliseconds];
        NSLog(@"The Timestamp is = %@",strTimestamp);
    }

 - (NSString *) GetUTCDateTimeFromLocalTime:(NSString *)IN_strLocalTime
    {
        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
        [dateFormatter setDateFormat:@"yyyy-MM-dd"];
        NSDate  *objDate    = [dateFormatter dateFromString:IN_strLocalTime];
        [dateFormatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"UTC"]];
        NSString *strDateTime   = [dateFormatter stringFromDate:objDate];
        return strDateTime;
    }

NOTE :- The Timestamp must be in UTC Zone, So I convert our local Time to UTC Time.

Swift

Updated for Swift 3

// current date and time
let someDate = Date()

// time interval since 1970
let myTimeStamp = someDate.timeIntervalSince1970

Notes

• timeIntervalSince1970 returns TimeInterval, which is a typealias for Double.

• If you wanted to go the other way you could do the following:

    let myDate = Date(timeIntervalSince1970: myTimeStamp)
  

If you want to store these time in a database or send it over the server...best is to use Unix timestamps. Here's a little snippet to get that:

+ (NSTimeInterval)getUTCFormateDate{

    NSDateComponents *comps = [[NSCalendar currentCalendar] 
                               components:NSDayCalendarUnit | NSYearCalendarUnit | NSMonthCalendarUnit 
                               fromDate:[NSDate date]];
    [comps setHour:0];
    [comps setMinute:0];    
    [comps setSecond:[[NSTimeZone systemTimeZone] secondsFromGMT]];

    return [[[NSCalendar currentCalendar] dateFromComponents:comps] timeIntervalSince1970];  
}

My preferred way is simply:

NSDate.date.timeIntervalSince1970;

As per @kexik's suggestion using the UNIX time function as below :

  time_t result = time(NULL);
  NSLog([NSString stringWithFormat:@"The current Unix epoch time is %d",(int)result]);

.As per my experience - don't use timeIntervalSince1970 , it gives epoch timestamp - number of seconds you are behind GMT.

There used to be a bug with [[NSDate date]timeIntervalSince1970] , it used to add/subtract time based on the timezone of the phone but it seems to be resolved now.

 [NSString stringWithFormat: @"first unixtime is %ld",message,(long)[[NSDate date] timeIntervalSince1970]];

 [NSString stringWithFormat: @"second unixtime is %ld",message,[[NSDate date] timeIntervalSince1970]];

 [NSString stringWithFormat: @"third unixtime is %.0f",message,[[NSDate date] timeIntervalSince1970]]; 

first unixtime 1532278070

second unixtime 1532278070.461380

third unixtime 1532278070

If you need time stamp as a string.

time_t result = time(NULL);                
NSString *timeStampString = [@(result) stringValue];