如何使用PHP计算上一个月的今天

echo date("Y-m-d H:i:s", mktime(date("G", $time), date("i", $time),
 date("s", $time), date("n", $time) - 1, date("j", $time), date("Y", $time)));

$time = strtotime("2011-03-31");
/
  计算上一个月的今天
  @param type $time
  @return type
 /
function last_month_today($time) {
     $last_month_time = mktime(date("G", $time), date("i", $time),
                date("s", $time), date("n", $time), - 1, date("Y", $time));
     return date(date("Y-m", $last_month_time) . "-d H:i:s", $time);
}
echo last_month_today($time);

 $time = strtotime("2011-03-31");
/
  计算上一个月的今天，如果上个月没有今天，则返回上一个月的一天
  @param type $time
  @return type
 /
function last_month_today($time){
    $last_month_time = mktime(date("G", $time), date("i", $time),
                date("s", $time), date("n", $time), 0, date("Y", $time));
    $last_month_t =  date("t", $last_month_time);
    if ($last_month_t < date("j", $time)) {
        return date("Y-m-t H:i:s", $last_month_time);
    }
    return date(date("Y-m", $last_month_time) . "-d", $time);
}
echo last_month_today($time);