Detect Json ecode error

gistfile1.php

$json  = json_encode($output);
switch (json_last_error()) {
    case JSON_ERROR_NONE:
        echo ' - No errors';
        break;
    case JSON_ERROR_DEPTH:
        echo ' - Maximum stack depth exceeded';
        break;
    case JSON_ERROR_STATE_MISMATCH:
        echo ' - Underflow or the modes mismatch';
        break;
    case JSON_ERROR_CTRL_CHAR:
        echo ' - Unexpected control character found';
        break;
    case JSON_ERROR_SYNTAX:
        echo ' - Syntax error, malformed JSON';
        break;
    case JSON_ERROR_UTF8:
        echo ' - Malformed UTF-8 characters, possibly incorrectly encoded';
        break;
    default:
        echo ' - Unknown error';
        break;
}