问PHP数组REST中的JSON编码和解码不起作用

EN

$transfer = {stdClass} [4]
    module = "Member"
    action = "create"
    token = null
    params = {stdClass} [3]
        username = "Test"
        email = "test@test.com"
        password = "Test"

{"module":"Member","action":"create","token":null,"params":{"username":"Test","email":"test@test.com","password":"Test"}}

{"module":"Member","action":"create","token":null,"params":{"username":"Test","email":"test@test.com" = ""

json_decode() expects parameter 1 to be string, array given

$curl = curl_init($url);

// prepare curl for Basic Authentication
curl_setopt($curl, CURLOPT_HTTPAUTH, CURLAUTH_BASIC);
curl_setopt($curl, CURLOPT_USERPWD, "$username:$password");

$curl_post_data = json_encode($postdata);
$test = json_decode($curl_post_data); // for testing

curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_POSTFIELDS, $curl_post_data); <= $postdata = $transfer the object/array mentioned above
$curl_response = curl_exec($curl);
curl_close($curl);