php字符串截取：按单词截取字符串，php截取字符串函数

<?php
function limit_words($string, $word_limit)
{
$words = explode(" ",$string);
return implode(" ",array_splice($words,0,$word_limit));
}
//Example Usage
$content = "Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.";
echo limit_words($content,20);
?>

/**
* 方法库-截取字符串-【该函数作者未知】
* @param string  $string 字符串 
* @param int$length 字符长度
* @param string  $dot截取后是否添加...
* @param string  $charset编码
* @return string
*/
public function cutstr($string, $length, $dot = ' ...', $charset = 'utf-8') {
   if (strlen($string) <= $length) {
  return $string;
   }
   $string = str_replace(array('&', '"', '<', '>'), array('&', '"', '<', '>'), $string);
   $strcut = '';
   if (strtolower($charset) == 'utf-8') {
  $n = $tn = $noc = 0;
  while ($n < strlen($string)) {
 $t = ord($string[$n]); //ASCII?
 if($t == 9 || $t == 10 || (32 <= $t && $t <= 126)) {
$tn = 1; $n++; $noc++;
 } elseif (194 <= $t && $t <= 223) {
$tn = 2; $n += 2; $noc += 2;
 } elseif (224 <= $t && $t < 239) {
$tn = 3; $n += 3; $noc += 2;
 } elseif (240 <= $t && $t <= 247) {
$tn = 4; $n += 4; $noc += 2;
 } elseif (248 <= $t && $t <= 251) {
$tn = 5; $n += 5; $noc += 2;
 } elseif ($t == 252 || $t == 253) {
$tn = 6; $n += 6; $noc += 2;
 } else {
$n++;
 }
 if($noc >= $length) {
break;
 }
  }
  if ($noc > $length) {
 $n -= $tn;
  }
  $strcut = substr($string, 0, $n);
   } else {
  for ($i = 0; $i < $length; $i++) {
 $strcut .= ord($string[$i]) > 127 ? $string[$i].$string[++$i] : $string[$i];
  }
   }
   $strcut = str_replace(array('&', '"', '<', '>'), array('&', '"', '<', '>'), $strcut);
   return $strcut.$dot;
}