php怎么实现转换为日期

$y=date("Y",time());         //年 $m=date("m",time());      //月 $d=date("d",time());        //日 echo $y." "; echo $m." "; echo $d." "; $eight_clock = mktime(8, 0, 0, $m, $d ,$y);  //每天8点 echo date("Y-m-d H:i:s",$eight_clock)." "; $day_time = mktime(0, 0, 0, $m, 1 ,$y);      //每月1号 echo date("Y-m-d H:i:s",$day_time)." ";

// convert a date into a string that tells how long ago // that date was.... eg: 2 days ago, 3 minutes ago. function ago($d) {  $c = getdate();  $p = array('year', 'mon', 'mday', 'hours', 'minutes', 'seconds');  $display = array('year', 'month', 'day', 'hour', 'minute', 'second');  $factor = array(0, 12, 30, 24, 60, 60);  $d = datetoarr($d);  for ($w = 0; $w < 6; $w++) {  if ($w > 0) {   $c[$p[$w]] += $c[$p[$w-1]] * $factor[$w];   $d[$p[$w]] += $d[$p[$w-1]] * $factor[$w];  }  if ($c[$p[$w]] - $d[$p[$w]] > 1) {    return ($c[$p[$w]] - $d[$p[$w]]).' '.$display[$w].'s ago';  }  }  return ''; } // you can replace this if need be.  // This converts my dates returned from a mysql date string  // into an array object similar to that returned by getdate(). function datetoarr($d) {  preg_match("/([0-9]{4})(\-)([0-9]{2})(\-)([0-9]{2})([0-9]{2})(\:)([0-9]{2})(\:)([0-9]{2})/",$d,$matches);  return array(   'seconds' => $matches[10],   'minutes' => $matches[8],   'hours' => $matches[6],   'mday' => $matches[5],   'mon' => $matches[3],   'year' => $matches[1],   ); }