php获取当前月份的前（后）几个月

//获取当前月份的前一月function GetMonth($sign) ?{ ?????//得到系统的年月 ?????$tmp_date=date("Ym"); ?????//切割出年份 ?????$tmp_year=substr($tmp_date,0,4); ?????//切割出月份 ?????$tmp_mon =substr($tmp_date,4,2); ?????// 得到当前月份的下几月 ???$tmp_nextmonth=mktime(0,0,0,$tmp_mon+$sign,1,$tmp_year); ?????// 得到当前月份的前几月 ???$tmp_forwardmonth=mktime(0,0,0,$tmp_mon-$sign,1,$tmp_year); ?????????return $fm_next_month=date("Ym",$tmp_forwardmonth); ?????????????}