http_build_query把数组转为&name=value字符串

parse_str 把&字符串转为数组

$arr=['tn' => 'monline_dg',
  'ie' => 'utf-8',
  'bs' => 'httpbuildurl', 
];
$url = http_build_query($arr);
echo($url);

$str = "f=3&rsv_bp=1&wd=php";
parse_str($str,$arr);
var_export($arr);