iOS中的NSDate

    NSDate *date = [NSDate date];
    NSLog(@"%@",date);//Thu Sep 13 16:16:13 2017

    NSDate *date1 = [date dateByAddingTimeInterval:5];
    NSLog(@"%@",date1);//Thu Sep 13 16:16:23 2017

    //获取系统的
    NSTimeZone *systemZone = [NSTimeZone systemTimeZone];
    //获取本地的
    NSTimeZone *localZone = [NSTimeZone localTimeZone];

NSInteger seconds = [systemZone secondsFromGMTForDate:date];
NSLog(@"%lu",seconds);//8小时

    NSDate *now = [NSDate date];
    
    NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
    formatter.dateFormat = @"yyyy-MM-dd HH:mm:ss z";
    NSString *dateStr = [formatter stringFromDate:now];
    NSLog(@"%@",dateStr);//2018-09-13 17:17:33 GMT+8

    NSString *dateString = @"2018-09-13 17:17:33 GMT+8";
    NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
    formatter.dateFormat = @"yyyy-MM-dd HH:mm:ss Z";
    NSDate *lastdDate = [formatter dateFromString:dateString];