why session variable is empty to navigate the next page? - php

Question

I have been working is a website I have been dealing with a problem from a while, and now I know why it is happening, but not how to solve it. Please help!!
Page 1:
In the first page, login page set the $_SESSION['user_id'] is stored the value that are fetch in database user id. In same page can print session and it work properly(the $_SESSION['user_id'] is print) and also navigate the next page(user home).
page 2:
In page 2(user home) the $_SESSION['user_id'] is turned into null value why this happen?
most probably see this problem in, forgot to set the session start but I was set session start both page...
page 1
<?php
if (isset($_POST['sub'])) {
$user = $_POST['user'];
$pass = $_POST['pass'];
$con = mysqli_connect("localhost", "root", "");
$db = mysqli_select_db($con, "Database");
$qry = "select * from TABLE where username='$user' and password='$pass'";
$res = mysqli_query($con, $qry) or die("could not connect to mysql");
$row = mysqli_fetch_array($res);
$len = mysqli_num_rows($res);
if ($len <= 0) {
echo "<script>";
echo "alert('Oops.Username Or Password Incorrect!');window.location.href='login.php';";
echo "</script>";
} else {
session_start();
$_SESSION['id'] = $row['id'];
$_SESSION['message'] = $user;
$_SESSION['logout'] = "";
$id = $_SESSION['id'];
echo "<script>";
echo "alert('log in Success $id ');window.location.href='login.php';"; //$id is print correctly
echo "</script>";
}
}
?>
page 2
<?php
ob_start();
session_start();
if (isset($_SESSION['id'])) {
$id = $_SESSION['id'];
echo "$user"; // not printed
}
if (isset($_SESSION['message'])) {
$msg = $_SESSION['message'];
$_SESSION['message'] = "";
}
if (isset($_SESSION['logout'])) {
$msg = $_SESSION['logout'];
if ($msg == 'logout') {
header("location:login.php");
$_SESSION['message'] = "you must login first";
exit(0);
}
}
?>
<?php
echo "welcome"; // only print this string the above session are not work
?>
I also use this code before some project and it work correctly then why this time the session value not working?

Answer 1

use session in the start in first page, like this. Hopefully this will work
<?php
session_start();
if (isset($_POST['sub']))
{
$user=$_POST['user'];
$pass=$_POST['pass'];
$con=mysqli_connect("localhost","root","");
$db=mysqli_select_db($con,"Database");
$qry="select * from TABLE where username='$user' and password='$pass'";
$res=mysqli_query($con,$qry)or die("could not connect to mysql");
$row=mysqli_fetch_array($res);
$len=mysqli_num_rows($res);
if($len<=0)
{
echo"<script>";
echo"alert('Oops.Username Or Password Incorrect!');window.location.href='login.php';";
echo"</script>";
}
else
{
$_SESSION['id']=$row['id'];
$_SESSION['message']=$user;
$_SESSION['logout']="";
$id=$_SESSION['id'];
echo"<script>";
echo"alert('log in Success $id ');window.location.href='login.php';"; //$id is print correctly
echo"</script>";
}
}
?>