Cannot modify header information - headers already sent

Question

Dear friends i am having strange error which i am unable to solve, need your help. The code is working fine when login is incorrect and when login is correct it still creates a session but do not redirect to index.php instead it throws an error of "Cannot modify header information - headers already sent by...". I already search for similar posts but was not able to solve the issue

here is the code

<?php include ("scripts/connection.php");
session_start();
$myusername = $_POST["myusername"];
$myusername = preg_replace('/[^a-zA-Z0-9\']/','',$_POST['myusername']);
$mypassword = $_POST["mypassword"];
$mypassword = preg_replace('/[^a-zA-Z0-9\']/','',$_POST['mypassword']);
$LoginQuery = "SELECT * FROM users WHERE username='$myusername' and password='$mypassword'";
?>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Admin Login</title>
</head>
<body>
<table width="300" border="0" align="center" cellpadding="0" cellspacing="1" bgcolor="#CCCCCC">
<tr><form name="form1" method="post">
<td>
<table width="100%" border="0" cellpadding="3" cellspacing="1" bgcolor="#FFFFFF">
<?php if($_SERVER["REQUEST_METHOD"] == "POST")
{ $result = $mysql->query($LoginQuery);
  if($result->num_rows ==1) 
{
$_SESSION['login_user']=$myusername;
header("Location:index.php");
exit();
}
else
{
echo '<tr><td width="78">&nbsp;</td><td width="6"></td><td width="294"><font style="color:#f00; font-weight:bold;">Invalid!</font></td></tr>';
}
}
?>
<tr>
<td colspan="3"><strong>Member Login </strong></td>
</tr>
<tr>
<td width="78">Username</td>
<td width="6">:</td>
<td width="294"><input name="myusername" type="text" id="myusername"></td>
</tr>
<tr>
<td>Password</td>
<td>:</td>
<td><input name="mypassword" type="text" id="mypassword"></td>
</tr>
<tr>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td><input type="submit" name="Submit" value="Login"></td>
</tr>
</table>
</td>
</form>
</tr>
</table>
</body>
</html>

Friends can u find what i did wrong and help me correct it please. Thank you

This error indeed strange. It has been answered 1000s times already and still people keep asking, despite of all the answers in the right column `--->` — Your Common Sense, Feb 17 '13 at 14:07

score 0 · Answer 1 · answered Feb 17 '13 at 14:08

0

you should use function header before writing any other text

answered Feb 17 '13 at 14:08

Solon

362
1
13

score 0 · Accepted Answer · answered Feb 17 '13 at 14:09

You have to understand HTTP:

A redirct is realized by the HTTP-Header. In HTTP the header is send, before any output (like the webpage itself)

So you are trying to send a Redirect-Header after you send payload.

This is not possible.

In short, never use header() after you print out something on the page.

Cannot modify header information - headers already sent

2 Answers2