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Editorial Team
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Asked: 2026-05-23T05:56:52+00:00

Today I learned for the first time how to create a simple login system

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Today I learned for the first time how to create a simple login system (with thanks StackExchange tips and THIS TUTORIAL. What i’m trying to do is use the PHPExcel framework to generate an Excel file ONLY for those who successfully login.

I’ve gotten very close, however I’m getting a crazy message about headers and below that is a bunch of jargon mixed up text.

Warning: Cannot modify header information - headers already sent by (output started at     /home3/mydir/public_html/d23/members/loggedin.php:6) in     /home3/mydir/public_html/d23/members/create_excel.php on line 92

Warning: Cannot modify header information - headers already sent by (output started at      /home3/mydir/public_html/d23/members/loggedin.php:6) in     /home3/mydir/public_html/d23/members/create_excel on line 93

Warning: Cannot modify header information - headers already sent by (output started at /home3/mydir/public_html/d23/members/loggedin.php:6) in /home3/mydir/public_html/d23/members/create_excel on line 94
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I know that the error is coming from these lines in the “create_excel.php” file, because when I comment them out, there is no error. But there is also no excel file creation. 

 header('Content-Type: application/vnd.ms-excel');
 header('Content-Disposition: attachment;filename="userList.xls"');
 header('Cache-Control: max-age=0');

I will outline my process step by step- i’m a beginner so I bet this is stupidly easy for someone.

STEP #1 (login.php)

Calls the “process_login.php” file to authenticate the password typed into the form.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"         "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Login Please</title>
</head>

<body>

<form action="process_login.php" method="post">
Password: <input type="password" name="password" /><br />
<input type="submit" value="Login" />
</form>

</body>
</html>

PAGE 2 (process_login.php)

If everything is fine,it will now re-direct you to “logged_in.php”, if not- you will get a denied message.

mysql_connect($host, $user, $pass);
mysql_select_db($database);


//$username = mysql_real_escape_string($_POST['username']);
$username = "person";
$password = hash('sha512', $_POST['password']);

$result = mysql_query("SELECT * FROM $table WHERE password = '$password'
");


if(mysql_num_rows($result))
{
  // Login
  session_start();
  $_SESSION['username'] = htmlspecialchars($username); // htmlspecialchars() sanitises     XSS
  // Redirect
header('Location: loggedin.php');
exit;
}
else
{
  echo '<p><strong>Error:</strong> Invalid username or password.</p>';
}
?>

STEP 3 (logged_in.php)

Now we have been successfully logged in, with an approval notice as well as a request to run “create_excel.php” file. 

<?php 
session_start();
if(isset($_SESSION['username']))
{
  // Logged in
  echo '<p>You are logged in as '. $_SESSION['username']. '.</p>';
   // require the PHPExcel file
require 'create_excel.php';

}
else
{
  // Not logged in
  echo '<p>You are not <a href="login.php">logged in</a>.</p>';
}
?>

STEP #4 (create_excel.php)

This is where the header problem happens. I’ve tried to put the session script on this page alone, but I get the same problem. I was thinking if it was pulled from the “logged_in” page everything would be fine- but no. (Currently if I access this page directly the Excel file is generated and downloaded no problem). 

<?php
/** Error reporting */
error_reporting(E_ALL);

date_default_timezone_set('Europe/London');

/** PHPExcel */
require_once 'Classes/PHPExcel.php';


// Create new PHPExcel object
$objPHPExcel = new PHPExcel();

// Set properties
$objPHPExcel->getProperties()->setCreator("Maarten Balliauw")
                             ->setLastModifiedBy("Maarten     Balliauw")
                             ->setTitle("Office 2007 XLSX Test     Document")
                             ->setSubject("Office 2007 XLSX Test     Document")
                             ->setDescription("Test document for         Office 2007 XLSX, generated using PHP classes.")
                             ->setKeywords("office 2007 openxml     php")
                             ->setCategory("Test result file");


// Add some data
$objPHPExcel->setActiveSheetIndex(0)
            ->setCellValue('A1', 'Hello')
            ->setCellValue('B2', 'world!')
            ->setCellValue('C1', 'Hello')
            ->setCellValue('D2', 'world!');

// Miscellaneous glyphs, UTF-8
$objPHPExcel->setActiveSheetIndex(0)
            ->setCellValue('A4', 'Miscellaneous glyphs')
            ->setCellValue('A5', 'éàèùâêîôûëïüÿäöüç');

// Rename sheet
$objPHPExcel->getActiveSheet()->setTitle('Simple');


// Set active sheet index to the first sheet, so Excel opens this as the first sheet
$objPHPExcel->setActiveSheetIndex(0);


// Redirect output to a client’s web browser (Excel5)
header('Content-Type: application/vnd.ms-excel');
header('Content-Disposition: attachment;filename="01simple.xls"');
header('Cache-Control: max-age=0');

$objWriter = PHPExcel_IOFactory::createWriter($objPHPExcel, 'Excel5');
$objWriter->save('php://output');
exit;
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1 Answer

  1. Editorial Team
      echo '<p>You are logged in as '. $_SESSION['username']. '.</p>';
  // require the PHPExcel file
  require 'create_excel.php';

    There lies your problem. You’re sending output to the client and then you want to change the headers and do something else. It doesn’t work that way.

    Consider doing it like this:

      echo '<p>You are logged in as '. $_SESSION['username']. '.</p>';
   // link to the PXPExcel file
  echo '<a href=\'create_excel.php\'>To Excel!</a>';

    Or just output the excel file without the login message:

      require 'create_excel.php';
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