日期字符串转换 and 两个日期相减

//创建当前日期
NSDate *date = [NSDate date];
//创建日期格式类
NSDateFormatter *dateFormat = [[NSDateFormatter alloc]init];
//设置日期格式
[dateFormat setDateFormat:@"yyyy/MM/dd HH:mm:ss"];
//获取招聘信息的创建日期
NSDate *createDate =[dateFormat dateFromString:_recruit.createTime];

NSLog(@"recruit.createTime==》%@ date==>：%@ - createDate:%@",recruit.createTime,date,createDate);

NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
unsigned int unitFlags = NSDayCalendarUnit;
NSDateComponents *comps = [gregorian components:unitFlags fromDate:createDate  toDate:date  options:0];
int days = [comps day];
NSLog(@"天数===%d",days);

打印：

recruit.createTime==》2014/5/7 14:57:49 date==>：2014-05-15 07:45:34 +0000 - createDate:2014-05-07 06:57:49 +0000