store $username and $file variables in the $_SESSION after login

Question

From **index.php** I get the values of the username and password fileds with $_POST

**index.php**

if(isset($_POST["username"]) && isset($_POST["password"])){

$username = mysql_real_escape_string(strtolower($_POST['username']));
$password = mysql_real_escape_string($_POST['password']);

$_SESSION['username'] = $username;
$_SESSION['password'] = $password;

checkUser($_SESSION['username'], $_SESSION['password']);
}

Then I store these $username and $password variables inside the $_SESSION and call a function checkUser($_SESSION['username'], $_SESSION['password'])); which sends two parameters. The checkUser() function executes inside **lib.php**

**lib.php**

session_start();

function checkUser($username, $password){
include "connection.php";
$result = mysqli_query($conn, "SELECT * FROM `data` WHERE `username` = '$username' AND `password` = '$password'") or die("No result".mysqli_error());

$row = mysqli_fetch_array($result);
$logic = false;

if (($row['username'] == $username) && ($row['password'] == $password)) {

$logic = true;

echo "HI,".$username;
?>

<a href='logout.php'>Log Out</a>

<?php

$file = $row['file'];
echo "<img src='images/users/".$file."' >";
}
else{
echo "Failed to login. Username or password is incorrect. Try again.";
}
}

This part is for showing the name of the user and the image according to it.

> logout.php works

**logout.php**

unset($_SESSION["username"]);
unset($_SESSION["password"]);
unset($_SESSION["file"]);
header("Location: index.php");

session_destroy();

**The problem is when I navigate from one page to another, the $_SESSION variable becomes empty. Something is wrong with session. Please help me.**

Answer 1

Have you included the sessions in every page?

Answer 2

Yes

Answer 3

may be you have included logout.php file to your each file .