php将日期格式转换成xx天前的格式

// 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],);
}