如果我取消注释session_start（）代码，页面将不会显示在浏览器上

这是包含会话代码的四个页面。当我运行sign_up.php页面时出现错误，指出该页面无法显示。因此，这些会议给我带来了一个问题。我在每个页面上都包含了会话代码，但是我相信问题出在header(location:........);任何解决方案上。

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._%+-][email protected]" 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 <a href="#">terms and condition</a>. <br/><br/>  

             <a href="#" class="button" style="margin-left: 600px; "><input type="submit" name="submit" value="Sign Up"/></a>
     </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._%+-][email protected]"  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

这是用户登录时的页面，该页面将允许他们访问其信息等。

   <?php
    session_start();
    if (!isset($_SESSION["user_login"])) {
       header("Location: sign_up.php");
    } else {
          $username = $_SESSION["user_login"];
    }

    include ("includes/connect.php");
    ?>

logout.php

这是我网站的注销代码

<?php


session_start();
session_destroy();
unset($_SESSION);
session_write_close();

header( "Location: ../index.php" );
die;
?>