//截取想這樣的字符串
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 ( $sourcestr ); //字符串的字節(jié)數(shù) 
   while ( ($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碼 
    if ($ascnum >= 224) {//如果ASCII位高與224，
       $returnstr = $returnstr . substr ( $sourcestr, $i, 3 ); //根據(jù)UTF-8編碼規(guī)范，將3個連續(xù)的字符計為單個字符  
       $i = $i + 3; //實際Byte計為3
       $n ++; //字串長度計1
    } elseif ($ascnum >= 192){ //如果ASCII位高與192，
       $returnstr = $returnstr . substr ( $sourcestr, $i, 2 ); //根據(jù)UTF-8編碼規(guī)范，將2個連續(xù)的字符計為單個字符 
       $i = $i + 2; //實際Byte計為2
       $n ++; //字串長度計1
    } elseif ($ascnum >= 65 && $ascnum <= 90) {//如果是大寫字母，
     $returnstr = $returnstr . substr ( $sourcestr, $i, 1 );
     $i = $i + 1; //實際的Byte數(shù)仍計1個
     $n ++; //但考慮整體美觀，大寫字母計成一個高位字符
    }elseif ($ascnum >= 97 && $ascnum <= 122) {
      $returnstr = $returnstr . substr ( $sourcestr, $i, 1 );
      $i = $i + 1; //實際的Byte數(shù)仍計1個
      $n ++; //但考慮整體美觀，大寫字母計成一個高位字符
    } else {//其他情況下，半角標點符號，
     $returnstr = $returnstr . substr ( $sourcestr, $i, 1 );
     $i = $i + 1; 
     $n = $n + 0.5; 
    }
   }
   return $returnstr;
}