setcookie（来自手册的例子）未设置

Question

Why setcookie is not work? I get data from database and try setcookie, but it is not set. I get example from php manual

$usrunic = $row['userunic'];
$usrfname=$row['first_name'];
$usrlname=$row['last_name'];
session_start();
$_SESSION['email']=$usremail;
$_SESSION['userid']=$usrunic;
$_SESSION['username']=$usrfname;
$_SESSION['userlname']=$usrlname;
if (!isset($_COOKIE[$usremail])){
setcookie($usremail,$usrunic,time()+3600);//1h
}