ios 如何获得系统时间和日期

//获得系统时间

NSDate * senddate=[NSDate date];

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

[dateformatter setDateFormat:@"HH:mm"];

NSString * locationString=[dateformatter stringFromDate:senddate];

//[dateformatter setDateFormat:@"YYYY-MM-dd-HH-mm-ss"];

//NSString * morelocationString=[dateformatter stringFromDate:senddate];

//获得系统日期

NSCalendar * cal=[NSCalendar currentCalendar];

NSUInteger unitFlags=NSDayCalendarUnit|NSMonthCalendarUnit|NSYearCalendarUnit;

NSDateComponents * conponent= [cal components:unitFlags fromDate:senddate];

NSInteger year=[conponent year];

NSInteger month=[conponent month];

NSInteger day=[conponent day];

NSString * nsDateString= [NSString stringWithFormat:@"%4d年%2d月%2d日",year,month,day];

[dateformatter release];

2.
从字符串来获得NSDate

string strYear="1988";

string strMonth="09";

string strDay="18";

string strHour="5";

string strMinutes="18";

string strSec="20";

morelocationString=[NSString stringWithFormat:@"%s-%s-%s-%s-%s-%s",strYear.c_str(),strMonth.c_str(),

strDay.c_str(),strHour.c_str(),strMinutes.c_str(),strSec.c_str()];

//根据时间字符串获得NSDate

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

[dateformatter setDateFormat:@"YYYY-MM-dd-HH-mm-ss"];

NSDate * oldDate=[dateformatter dateFromString:morelocationString];

3. 从GMT时间，得到本地时间

NSDate * oldDate=[dateformatter dateFromString:morelocationString];

NSTimeInterval timeZoneOffset=[[NSTimeZone systemTimeZone] secondsFromGMT];

NSDate * newDate=[oldDate dateByAddingTimeInterval:timeZoneOffset];