php自定义中文字符串截取函数substr_for_gb2312及substr_for_utf8示例

/**gb2312中文字符串截取 */function substr_for_gb2312($str,$start,$len=null) {  $totlelength = strlen($str);  //特例情况  if ($len == null) $len = $totlelength;  if ($len ==0) return "";  if ($len >= $totlelength && $start == 0 ) return $str;  if ($start > $totlelength) return "";  //分析$start  if ($start < 0 ) //$start<0时,转化为$start>0时的定位.  {  if ( abs($start) >= $totlelength ) $start = 0;  else $start = $totlelength - abs($start);  }  //确定起始位置,当起始位拆分某汉字时,返回值包含此汉字.  if ($start > 0)  {  $i = $start-1;  $flag = -1;  while ($i >= 0)  {  if ( ord(substr($str,$i,1)) > 160)  {  $flag = -1*$flag;  }  else break;  $i--;  }  if($flag==1)  {  $start = $start - 1;  $len++;    //保证不位移.  } } $str = substr($str,$start);//截除字符串$str的$start位前的字符 $totlelength = strlen($str); //确定结束位置,当结束位拆分某汉字时,返回值不包含此汉字. if ($len<0) $len = $totlelength - abs($len); if ($len <= 0) return ""; $i=min($len,$totlelength); $i--; $flag = -1; while ($i >= 0) {  if (ord(substr($str,$i,1))>160)  {   $flag=-1*$flag;  }  else break;  $i--; } if($flag == 1)  $len=$len-1; $subit=substr($str,0,$len); return $subit; }/******************************************************************* PHP截取UTF-8字符串，解决半字符问题。* 英文、数字（半角）为1字节（8位），中文（全角）为3字节* @return 取出的字符串, 当$len小于等于0时, 会返回整个字符串* @param $str 源字符串* $len 左边的子串的长度****************************************************************/function substr_for_utf($str,$len){for($i=0;$i<$len;$i++){$temp_str=substr($str,0,1);if(ord($temp_str) > 127){$i++;if($i<$len){$new_str[]=substr($str,0,3);$str=substr($str,3);}}else{$new_str[]=substr($str,0,1);$str=substr($str,1);}}return join($new_str);}?>/*带start位置的utf8截取函数*/function utf8_substr($string, $start, $length) {  preg_match_all ('/[/x00-/x7F]|[/xC2-/xDF][/x80-/xBF]|[/xE0-/xEF][/x80-/xBF][/x80-/xBF]|[/xF0-/xF4][/x80-/xBF][/x80-/xBF][/x80-/xBF]/', $string, $rs);  $out = '';  $size = count ($rs[0]);  $end = $start + $length;  if ($end > $size ) {    $end = $size;  }  for ($i = $start; $i < $end; $i++) {    $out .= $rs[0][$i];  }  return $out;}