问如何在低于5.3.0的PHP中验证JSON？

EN

$ob = json_decode($json);
if($ob === null) {
 // $ob is null because the json cannot be decoded
}

$data = json_decode($json_string);
if (is_null($data)) {
   die("Something dun gone blowed up!");
}

if (!function_exists('json_last_error_msg')) {
        function json_last_error_msg() {
            static $ERRORS = array(
                JSON_ERROR_NONE => 'No error',
                JSON_ERROR_DEPTH => 'Maximum stack depth exceeded',
                JSON_ERROR_STATE_MISMATCH => 'State mismatch (invalid or malformed JSON)',
                JSON_ERROR_CTRL_CHAR => 'Control character error, possibly incorrectly encoded',
                JSON_ERROR_SYNTAX => 'Syntax error',
                JSON_ERROR_UTF8 => 'Malformed UTF-8 characters, possibly incorrectly encoded'
            );

            $error = json_last_error();
            return isset($ERRORS[$error]) ? $ERRORS[$error] : 'Unknown error';
        }
    }