NSDate比较

        NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
        NSDate * oldDate = [uidSCDictNew objectForKey:userIDForBlogNew];
        NSDate * newDate = [NSDate date];
        
        NSCalendar *newcalendar = [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] autorelease];
        NSCalendar *oldcalendar = [[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar] autorelease];
        NSDateComponents *newcomps = [[[NSDateComponents alloc] init] autorelease];
        NSDateComponents *oldcomps = [[[NSDateComponents alloc] init] autorelease];
        NSInteger unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit;
 
        newcomps = [newcalendar components:unitFlags fromDate:newDate];
        oldcomps = [oldcalendar components:unitFlags fromDate:oldDate];
        int newyear=[newcomps year];
        int newmonth = [newcomps month];
        int newday = [newcomps day];
        int oldyear=[oldcomps year];
        int oldmonth = [oldcomps month];
        int oldday = [oldcomps day];
        BOOL bsameDay = YES;
        if (newyear > oldyear)
        {
            bsameDay = NO;
        }
        else
        {
            if (newmonth > oldmonth)
            {
                bsameDay = NO;
            }
            else
            {
                if (newday > oldday)
                {
                    bsameDay = NO;
                }
                else
                {
                    bsameDay = YES;
                }
            }
            
        }
        
        //时间比较，非同一天
        if (!bsameDay)
        {
           //
        }
        else//同一天
        {
           
        }
        [pool release];