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Accepted
Pavlo B.
Asked: 2020-11-10 01:42:14 +0800 CST 2020-11-10 01:42:14 +0800 CST

Header error - Warning: Cannot modify header information - headers already sent

  • 772

This is the error:

Warning: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\newop\template\header.php:80) in C:\xampp\htdocs\newop\mainindex.php on line 16

Line 80 of the header is this (it's a single line, only unpacked):

<div class="col-md-2 col-xs-2 device-select">
    <a href="budget.php?device=2">
        <img class="full-width" src="res/images/device2.jpg">
        </img>
    </a>
    <center class="popular-devices">
<?php echo $lang['header_dropdown_string_2'];?>
    </center>
</div>

... and this the code:

<?php
session_start();
if (!isset($_SESSION['user'])){ header("Location: index.php"); }
?>
<html>
  <body>
<?php
  include("template/head.php");
  include("template/header.php");
  include ("db_files/db.php");
  $usermail = mysqli_real_escape_string($db, $_SESSION['user']);
  $strSQL = "SELECT nivel FROM usuarios where email ='$usermail'";
  $query = mysqli_query($db, $strSQL);
  while ($result = mysqli_fetch_array($query)){
    if ($result['nivel'] == 1 || $result['nivel'] == 2){
    header("location: userlist:php");
  }
  
}
  $state = array(
    1 => $lang['state_name_string_1'],
    2 => $lang['state_name_string_2'],
    3 => $lang['state_name_string_3'],
    4 => $lang['state_name_string_4'],
  );
?>
  <div class="content container">
    <div class="row no-margin no-padding">
      <div class="col-md-2 hidden-sm hidden-xs">
        <div class="mainuserimage">
          <img class="full-width" src="res/images/users/user1.png"/>
        </div>
        <div>
<?php
            $strSQL = "SELECT nombre, email, telefono FROM usuarios where email ='$usermail'";
            $query = mysqli_query($db, $strSQL);
            while ($result = mysqli_fetch_array($query)){
              echo "<i class='glyphicon glyphicon-user'></i> ".$result['nombre']."<br>";
              echo "<i class='glyphicon glyphicon-envelope'></i> ".$result['email']."<br>";
              echo "<i class='glyphicon glyphicon-earphone'></i> ".$result['telefono']."<br>";
            }
?>
        </div>
      </div>
      <div class="col-md-10 col-xs-12">
      <h3 class="main-title"><?php echo $lang['mainindex_string_1']; ?></h3><br>
        <div class="row">
          <div class="col-md-2 col-xs-3">
            <p><?php echo $lang['mainindex_string_2']; ?></p>
          </div>
          <div class="col-md-2 col-xs-3">
            <p><?php echo $lang['mainindex_string_3']; ?></p>
          </div>
          <div class="col-md-2 col-xs-3">
            <p><?php echo $lang['mainindex_string_4']; ?></p>
          </div>
          <div class="col-md-2 hidden-sm hidden-xs">
            <p><?php echo $lang['mainindex_string_5']; ?></p>
          </div>
          <div class="col-md-2 col-xs-3">
            <p><?php echo $lang['mainindex_string_6']; ?></p>
          </div>
          <div class="col-md-2 hidden-sm hidden-xs">
            <p><?php echo $lang['mainindex_string_7']; ?></p>
          </div>
<?php
            $strSQL = "SELECT id, marca, modelo, imei, descripcion_problema, problem, problem2, problem2_namees, estado, fecha_creacion FROM tickets, problem2 WHERE tickets.email = '$usermail' AND tickets.problem2 = problem2.problem2_id";
            $query = mysqli_query($db, $strSQL);
            while($result = mysqli_fetch_array($query)){ ?>
              <div class="col-md-2 col-xs-3">
                <p><a href="repairdetail.php?id=<?php echo $result['id']; ?>"><i class="glyphicon glyphicon-list-alt"></i></a>  <?php echo $result['marca']; ?></p>
              </div>
              <div class="col-md-2 col-xs-3">
                <p><?php echo $result['modelo']; ?></p>
              </div>
              <div class="col-md-2 col-xs-3">
                <p><?php echo $result['imei']; ?></p>
              </div>
              <div class="col-md-2 hidden-sm hidden-xs">
                <p><?php echo $result['problem2_namees']; ?></p>
              </div>
              <div class="col-md-2 col-xs-3">
                <p><?php echo $state[$result['estado']]; ?></p>
              </div>
              <div class="col-md-2 hidden-sm hidden-xs">
                <p><?php echo $result['fecha_creacion']; ?></p>
              </div>
<?php
            }
?>
          </div>
        </div>
    </div>
  </div>
<?php
  include("template/footer.php");
?>
  </body>
</html>

php

2 Answers

  1. Best Answer

    Move the block:

    include ("db_files/db.php");
$usermail = mysqli_real_escape_string($db, $_SESSION['user']);
$strSQL = "SELECT nivel FROM usuarios where email ='$usermail'";
$query = mysqli_query($db, $strSQL);

while ($result = mysqli_fetch_array($query)){
    if ($result['nivel'] == 1 || $result['nivel'] == 2){
        header("location: userlist.php"); //<= Error: userlist:php !!!
    }
}

    prior to:

    <html>
...

    PHP functions that send or modify HTTP headers must be executed before the requested page has started to be sent to the user.

    Additional information about the error: - headers already sent

    A message HTTPconsists of a header - Headerand a body - Bodywhich are sent to the client in this order Client. At the time the is sent, the Bodycan no longer be sent Header.

    If you then try to call the function header()after it has been sent HTML, you will get the famous error: Cannot modify header information - headers already sent.

    Not only the header() function modifies the Headerbut also the following functions:

    Other examples which also produce an error before sending the Header:

    • spaces before opening_<?php
    • Spaces after closing?>_
    • Use UTF-8 with BOM
    • Show/add information/content or error messages:
      HTML, echo, print, var_dump()....etc

    Examples of erroneous codes:

    <?php
echo "Foo Bar"; // Mostrar contenido echo
setcookie("Foo", "Bar");

     <?php // Espacio antes del "<?php"
session_start();
?>

    <html> <!-- Mostrando contenido HTML -->
<head>
<?php
session_start();
?>
    • 13

  2. The error occurs because you are sending the html output before modifying the header, so the default headers have already been sent.

    You can fix this by moving the html block after the header command. Or also using the function ob_start()in the first lines of code. That will start the output buffer cache and the headers will not be sent until the script is finished.

    • 4