string json in object php code example

Example 1: return json in php

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

Example 2: php is json

function is_json($input_line) {
    if(is_string($input_line)){
        preg_match('/^\{(\s+|\n+)*(\"(.*)(\n+|\s+)*)*\}$|^\[(\s+|\n+)*\{(\s+|\n+)*(\"(.*)(\n+|\s+)*)*\}(\s+|\n)*\]$/', $input_line, $output_array);
        if (  isset($output_array) || !empty($output_array)) {
            return true;
        }
    }
    return false;
    }