PHP Functions - arsort()

 <?php

 $characters = array('a','b','c','d','e','f');
 arsort($characters);
 print_r($characters);
 /*
     Array ( [5] => f [4] => e [3] => d [2] => c [1] => b [0] => a )
 */

 $numbers = array(1,2,3,4,5,6,7,8);
 arsort($numbers);
 print_r($numbers);
 /*
 Array ( [7] => 8 [6] => 7 [5] => 6 [4] => 5 [3] => 4 [2] => 3 [1] => 2 [0] => 1 )
 */

 $fruits = array('lemon' , 'orange' ,'banana' , 'apple');
 arsort($fruits);
 print_r($fruits);
 /*
 Array ( [1] => orange [0] => lemon [2] => banana [3] => apple )
 */

 /*arsort()函数对中文的排序结果*/
 $chinese = array('爱','本','吃','地');//ai-ben-chi-di
 var_dump(arsort($chinese));
 print_r($chinese);
 /*
     bool(true)
     Array ( [0] => 爱 [1] => 本 [3] => 地 [2] => 吃 )
 */

 $pingyin = array('ai','ben','chi','di');
 arsort($pingyin);
 print_r($pingyin);
 /*
     Array ( [3] => di [2] => chi [1] => ben [0] => ai )
 */
 ?>

结论：[单元索引关系不变，逆序排序]

　　1.对英文字符排序是按照27个英文字母排列顺序进行逆序排列，单元索引关系保持不变；

　　2.对数字排序是按照数字顺序进行逆序排列，单元索引关系保持不变；

问题：arsort()函数究竟是怎么对中文文字进行排序的