How can I get and print correctly a session in php? -

i have php start session if $msj "si" :

<?php  require "dao/daologinusu.php";    class loginusuario{      public function setdatos($ainput) {          $obj = json_decode($ainput, true);         $dao = new daologinusuario();        $dao->setdatadato($obj);         $msj = $dao->setdatadato($obj);         if($msj == 'si'){         session_start();          $_session['msj'] = 'si';        }        return $msj;            }          }     ?> 

and in php want print session :

<?php  session_cache_limiter(false); session_start(); print_r($_session); 

and then..

if($_session['msj'] == 'si'){..... 

but when "si" print_r($_session); print:

    array (     [slim.flash] => array         (         )  ) 

why can't print session?

the $_session global array in php, array, can outputted using var_dump(). formatting makes output more readable.

echo '<pre>'; var_dump($_session); echo '</pre>';