<?php

$a1=array("a"=>"red","b"=>"green","c"=>"blue","d"=>"yellow");

$a2=array("a"=>"red","b"=>"green","c"=>"blue");

$result=array_intersect_assoc($a1,$a2);

print_r($result);

?>

Array ( [a] => red [b] => green [c] => blue )

parse_str(string,array)
string 必需。规定要解析的字符串。
array  可选。规定存储变量的数组的名称。该参数指示变量将被存储到数组中。

在subject中搜索pattern， 以replacement进行替换。
preg_replace ( mixed $pattern , mixed $replacement , mixed $subject [, int $limit = -1 [, int &$count ]] )