php 截取中英文混合字符串的方法

//截取想这样的字符串a李三

/** *  * 中英混合的字符串截取 * @param unknown_type $sourcestr * @param unknown_type $cutlength */function assoc_substr($sourcestr, $cutlength) {   $returnstr = '';   $i = 0;   $n = 0;   $str_length = strlen ( $sourcestr ); //字符串的字节数    while ( ($n < $cutlength) and ($i <= $str_length) ) {    $temp_str = substr ( $sourcestr, $i, 1 );    $ascnum = Ord ( $temp_str ); //得到字符串中第$i位字符的ascii码     if ($ascnum >= 224) {//如果ASCII位高与224，       $returnstr = $returnstr . substr ( $sourcestr, $i, 3 ); //根据UTF-8编码规范，将3个连续的字符计为单个字符         $i = $i + 3; //实际Byte计为3       $n ++; //字串长度计1    } elseif ($ascnum >= 192){ //如果ASCII位高与192，       $returnstr = $returnstr . substr ( $sourcestr, $i, 2 ); //根据UTF-8编码规范，将2个连续的字符计为单个字符        $i = $i + 2; //实际Byte计为2       $n ++; //字串长度计1    } elseif ($ascnum >= 65 && $ascnum <= 90) {//如果是大写字母，     $returnstr = $returnstr . substr ( $sourcestr, $i, 1 );     $i = $i + 1; //实际的Byte数仍计1个     $n ++; //但考虑整体美观，大写字母计成一个高位字符    }elseif ($ascnum >= 97 && $ascnum <= 122) {      $returnstr = $returnstr . substr ( $sourcestr, $i, 1 );      $i = $i + 1; //实际的Byte数仍计1个      $n ++; //但考虑整体美观，大写字母计成一个高位字符    } else {//其他情况下，半角标点符号，     $returnstr = $returnstr . substr ( $sourcestr, $i, 1 );     $i = $i + 1;      $n = $n + 0.5;     }   }   return $returnstr;}