OC笔记NSDate

```python

//-----1--NSDate -------

//NSDate的定义

NSDate * nowDate = [NSDate date];

NSLog(@"%@",nowDate);

//NSDateFormatter的定义

NSDateFormatter *df = [[NSDateFormatter alloc]init];

//日期的加减运算

nowDate = [nowDate dateByAddingTimeInterval:-5 * 60 * 60];

NSLog(@"%@",nowDate);

[df setDateFormat:@"dd/MM yyyy HH:mm:ss"];

NSString *dateStr = [df stringFromDate:nowDate];

NSLog(@"%@",dateStr);

```