NSDateFormatter用法：

日期格式化是最基本的了，就是那些套路，下面列一下：

NSDateFormatter * dateFormatter = [[[NSDateFormatter alloc] init]autorelease];

[dateFormatter setAMSymbol:@"AM"];

[dateFormatter setPMSymbol:@"PM"];

[dateFormatter setDateFormat:@"yyyy年MM月dd日 hh:mmaaa"];

NSDate *date = [NSDate date];

NSString * s = [dateFormatter stringFromDate:date];

显示效果为：2012年09月01日 03:49PM

下面附上几个格式：这个是从Cocoachina上来的

yyyy:MM:dd G 'at' HH:mm:ss zzz            1996.07.10 AD at 15:08:56 PDT

EEE, MMM d, "yy                                         Wed,july 10, '99

h:mm a                                                     12:08 PM

hh 'o"clock' a,zzzz                                      12 o'clock PM, Pacific Daylight Time

K:mm a, z                                                 0:00 PM, PST

yyyyy,MMMM.dd GGG hh:mm aaa                01996.july.10 AD 12:08 PM

下面是得到当前的年，月，日，时，分，秒。

NSCalendar *cal = [NSCalendar currentCalendar];

unsigned int unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;

NSDateComponents *dd = [cal components:unitFlags fromDate:date]; 

int y = [dd year];

int m = [dd month];

int d = [dd day];

int h = [dd hour];

int m = [dd minute];

int s = [dd second];