Page doesnt display on browser if i uncomment the session_start() code - php

Question

These are the four pages which include the code for sessions. when i run the sign_up.php page an error comes up stating the page cannot be displayed. So the sessions are giving me an problem. I have included the session code on each page however i believe the problem is in the header(location:........); So any solutions please.
sign_up.php
<?php
//session_start();
//if (!isset($_SESSION["user_login"])) {
// header("Location: sign_up.php");
//} else {
// $username = $_SESSION["user_login"];
//}
?>
<!----------------------------------------------------------------------------------------------------->
<h1> Sign Up </h1>
<hr>
<div class = "user_type">
<form action="sign_up.php" method="POST" enctype="multipart/form-data">
<input type="radio" value="Student" id="radioOne" name="account" checked/>
<label for="radioOne" class="radio" chec>Student </label>
<input type="radio" value="Landlord" id="radioTwo" name="account" />
<label for="radioTwo" class="radio">Landlord</label>
<hr/>
<div class = "gender_options">
<input type="radio" value="Male" id="male" name="gender" checked/>
<label for="male" class="radio" chec>Male</label>
<input type="radio" value="Female" id="female" name="gender" />
<label for="female" class="radio">Female</label>
</div>
<input type="text" name="name" id="name" placeholder="Full Name" required/> <br/><br/>
<input type="email" name="email" id="name" placeholder="Email" pattern="[a-z0-9._%+-]+#aston.ac.uk" required/> <br/><br/>
<input type="text" name="password" id="name" placeholder="Password" required/><br/><br/>
<input type="text" name="password2" id="name" placeholder="Retype Password" required/><br/><br/>
By clicking Sign Up, you agree on our terms and condition. <br/><br/>
<input type="submit" name="submit" value="Sign Up"/>
</form>
</div>
<hr>
<!---- log in code--->
<?php
enter code here
if (isset($_POST["user_login"]) && isset ($_POST["user_pass"])){
// formatting field via reg replace to ensure email and password only conisists of letters and numbers preg_replace('#[^A-Za-z0-9]#i','',
$login_user = $_POST["user_login"];
$login_password = $_POST["user_pass"];
// password is encryted in DB (MD5) therefore user inputted password will not match encryted password in DB - we have to assign new var
$decrypted_password = md5($login_password);
// Query which finds user (if valid) from DB - Achieving authentication via username and password
$user_query = mysqli_query($connect, "SELECT * FROM users WHERE email = '$login_user' AND password = '$decrypted_password' AND closed = 'no' LIMIT 1");
$check_user = mysqli_num_rows($user_query); // checking to see if there is infact a user which those credentials in the DB
if ($check_user==1){
while ($row = mysqli_fetch_array($user_query)){
$id = $row['user_id'];
}
enter code here
// if the user credentials are correct, log the user in:
$_SESSION["user_login"] = $login_user;
header( "Location: profile_student.php" ); // refresh page
exit;
// if user row does not equal 1 ...
//exit;
} else {
echo "<div class='wrong_login'>
<p> Email or password is incorrect, please try again. </p>
</div>";
}
}
?>
<h1> Log In </h1>
<hr>
<div class ="login_form">
<form action="sign_up.php" method="POST">
<input type="text" name="user_login" placeholder="Email" pattern="[a-z0-9._%+-]+#aston.ac.uk" required/><br/><br/>
<input type="text" name="user_pass" placeholder="Password" required/> <br/><br/>
<input type="submit" name="login_submit" value="Log In"/>
</form>
</div>
</div>
home.php
<?php
session_start();
if (!isset($_SESSION["user_login"])) {
header("Location: profile_student.php");
} else {
$username = $_SESSION["user_login"];
}
include ("connect.php");
echo "Hello,";
echo"<br/> Would you like to logout? <a href = 'logout.php'>LogOut</a>";
?>
profile_student.php
This is the page for when the user logs in and this page will allow them to access their information etc.
<?php
session_start();
if (!isset($_SESSION["user_login"])) {
header("Location: sign_up.php");
} else {
$username = $_SESSION["user_login"];
}
include ("includes/connect.php");
?>
logout.php
this is the log out code for my website
<?php
session_start();
session_destroy();
unset($_SESSION);
session_write_close();
header( "Location: ../index.php" );
die;
?>

Answer 1

Instead of doing the session_start in each page, make a common.php file and include this file in all the required pages. Also, you need to make sure there is no white space before session is started, otherwise it would throw the header already sent error!

Answer 2

You are true, the problem is the header.
You are creating an infinite loop saying : you come on sign_up ? If $_SESSION['user_login'] doesnt exist, go to sign_up.
And it repeats over and over again. Because $_SESSION['user_login'] cant exist first time you come on sign_up.
So just do this : on your sign_up page.
<?php
session_start();
And so remove the if / else condition.