Answers for "php get correct json string"

php is json string

function IsJsonString(str) {
    try {
        JSON.parse(str);
    } catch (e) {
        return false;
    }
    return true;
}

return json in php

//code igniter
$query="qry";
$query = $this->db->query($query);
$res=$query->result();
return json_encode($res);