如何在php上获取json的元素？

When I use var_dump($_POST), I get this:

array(2) {
  ["param"]=>
  string(327) "{"username":"asd","password":"asdasd","language":"7"}"
}

I need to get username. I've tried it this:

$arr = json_decode($_POST['param'], true);
echo $arr["username"];

But it doesn't work.

Anyone know where my error is and what the right way to get element username is?

Please check the edited answer:

$arr = json_decode($_POST['param'],true);
echo $arr['username'];

Your jason encoded string seems to be inside the param element, Try this:

$arr = json_decode($par['param'], true);
echo $arr["username"];