将登录页面上传到在线服务器后，登录页面无效[重复]

Question

This question already has an answer here:

• How to fix “Headers already sent” error in PHP 11 answers

After entering username and password, showing this eror

Warning: Cannot modify header information - headers already sent by (output started at /storage/****************/public_html/Include/Header.php:1) in /****************/public_html/user_login.php on line 17

in localserver it works fine but after uploading to 000webhost it gives the above error

please help me, thanks

<?php 
session_start();
include("/storage/****************/public_html/Include/Header.php"); 
include('/storage/****************/public_html/Include/Navbar.php');
include('/storage/****************/public_html/Include/db.php');


    ?>
       <?php
   if(isset($_POST['submit'])){
       $u_username=$_POST['u_username'];
       $u_password=$_POST['u_password'];
       $sql=mysqli_query($link, "SELECT * FROM tbl_user where u_username='$u_username' and u_password='$u_password'");
       $result=mysqli_fetch_array($sql);
       if($result['u_username']== $u_username and $result['u_password']== $u_password){
           $_SESSION['user']=$u_username;
             header("location:/storage/****************/public_html/123.php");


       }else{

           $error= "<div class='alert alert-danger'>ID or Password Incorrect</div>";

       }

   }

  ?>

   <div class="row">
    <!-- Collect the nav links, forms, and other content for toggling -->
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">

            <ul class="nav navbar-nav navbar-left" id="nav">
                <li><a href="index.php"><i class="fa fa-home"></i> Home</a></li>

            </ul></div>


    </div><!-- /.navbar-collapse -->
  </div><!-- /.container-fluid -->
</nav>
   <!--Main Body-->
     <div class="container">
         <div class="panel panel-primary col-md-9">
            <div class="panel-heading">
                <h3>Admin Login</h3>
            </div>
            <div class="panel-body col-md-7">
              <form class="form-horizontal" action="" method="post">
             <div class="form-group">
                 <label for="Name" class="col-md-5">Your username: *</label>
                 <div class="col-md-7">
                     <input type="text" required name="u_username" class="form-control" placeholder="Your ID Here...">
                 </div>
             </div>
            <div class="form-group">
                 <label for="Name" class="col-md-5">Your Password: *</label>
                 <div class="col-md-7">
                     <input type="Password" name="u_password" class="form-control" placeholder="Your Password Here..." required>
                 </div>
             </div>
             <div class="form-group">
                 <label for="Name" class="col-md-5"></label>
                 <div class="col-md-7 ">
                     <?php if(isset($error)){
                            echo $error; }?>
                 </div>
             </div>
             <div class="form-group">
                 <label for="Name" class="col-md-5"></label>
                 <div class="col-md-7">
                     <input type="submit" name="submit" value="Login" class="btn btn-success btn-block">
                 </div>
             </div>

            <div>
                <h3>Note:</h3> 
                <p>If NOT Registered! Please <a href="contact.php">Contact Us</a>.</p>
            </div>


                </form>


         </div>

     </div>
</div><br>

   <!--End of Main Body-->
   <?php 
include("/storage/****************/public_html/Include/Footer.php")
?>

</div>

Answer 1

After the includes, remove the two following lines :

?>
   <?php

Because, between close tag and open tag, there is multiple spaces sent to the output, which causes this warning.

Finally, add exit() after header() to stop the script.