<?php

//例举一个URL格式的字符串:
$str = 'http://test.com/testdir/index.php?param1=10&param2=20&param3=30&param4=40&param5=50&param6=60';

//1 用parse_url解析URL,此处是$str
$arr = parse_url($str);
var_dump($arr);

//2 将URL中的参数取出来放到数组里
$arr_query = convertUrlQuery($arr['query']);
var_dump($arr_query);

//3 将 参数数组 再变回 字符串形式的参数格式
var_dump(getUrlQuery($arr_query));


/**  
  * Returns the url query as associative array  
  * @param     string     query  
  * @return     array     params  
  */  
function convertUrlQuery($query)
{
    $queryParts = explode('&', $query);
    $params = array();
    foreach ($queryParts as $param)
    {
        $item = explode('=', $param);
        $params[$item[0]] = $item[1];
    }
    return $params;
}

function getUrlQuery($array_query)
{
    $tmp = array();
    foreach($array_query as $k=>$param)
    {
        $tmp[] = $k.'='.$param;
    }
    $params = implode('&',$tmp);
    return $params;
}
?>

输出结果：

array (size=4)
  'scheme' => string 'http' (length=4)
  'host' => string 'test.com' (length=8)
  'path' => string '/testdir/index.php' (length=18)
  'query' => string 'param1=10&param2=20&param3=30&param4=40&param5=50&param6=60' (length=59)


array (size=6)
  'param1' => string '10' (length=2)
  'param2' => string '20' (length=2)
  'param3' => string '30' (length=2)
  'param4' => string '40' (length=2)
  'param5' => string '50' (length=2)
  'param6' => string '60' (length=2)


string 'param1=10&param2=20&param3=30&param4=40&param5=50&param6=60' (length=59)