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:];
    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