PHP Warning : cannot modify header information [duplicate] - php

Question

This question already has answers here:
How to fix "Headers already sent" error in PHP
(11 answers)
Closed 9 years ago.
I have an php login function. When I try to logged in with correct user, it show the error like this :
Warning: Cannot modify header information - headers already sent by (output started at /home/hapshou1/public_html/index.php:15) in /home/hapshou1/public_html/index.php on line 150
-
include "config.php";
if($_SERVER["REQUEST_METHOD"] == "POST")
{
function antiinjection($data)
{
$filter_sql = mysql_real_escape_string(stripslashes(strip_tags(htmlspecialchars($data,ENT_QUOTES))));
return $filter_sql;
}
$username = antiinjection($_POST['username']);
$pass = antiinjection($_POST['password']);
$login=mysql_query("SELECT username, password FROM user WHERE (username='$username' OR email='$username') AND password='$pass'");
$found=mysql_num_rows($login);
$r=mysql_fetch_array($login);
if
((!empty($username)) &&
(!empty($pass)))
{
if ($found > 0)
{
session_register("username");
session_register("password");
$_SESSION[username] = $r[username];
$_SESSION[password] = $r[password];
date_default_timezone_set("Asia/Jakarta");
$date_log = date("j-F-Y, G:i ");
mysql_query("update user set status='online', date_logged_in='$date_log' WHERE username='$_SESSION[username]'");
header('location:home');
}
else
{
echo '<div class="error_log">
<p>Wrong username or password. Please try again.</p>
</div>';
}
}
else
{
echo '
<div class="error_log">
<p>Username and password are required.</p>
</div>
';
}
}
What's wrong with my code?

Answer 1

Well, then look at what's on line 15.
The most likely scenario is that this statement caused the output:
$found=mysql_num_rows($login);
Which in turn is caused by the fact that your mysql_query returns false.
You could consider this to report any errors:
if (false === ($login=mysql_query("SELECT username, password FROM user WHERE (username='$username' OR email='$username') AND password='$pass'"))) {
die(mysql_error());
}
It's not advisable to use die() statements like this in a production environment, so consider using a logger instead
Btw, learn how to use PDO / mysqli; PDO has a mode in which all errors can be turned into exceptions which helped me find bugs much faster.

Answer 2

Put ob_start(); at top of the code and put ob_flush(); at end
Always put exit(); after header redirect

Answer 3

Enclose your code within
ob_start();
...
ob_flush();
The reason this error occurs is that some part of the body of the web page has been sent to the user already when a request is made to set a header value.
Also always put exit(); after header() statement so that rest of code on current page after the header() call doesn't get executed.

Answer 4

Exemple: header('Location: http://www.example.com/');
Naga, try this code:
session_start();
date_default_timezone_set("Asia/Jakarta");
include "config.php";
if(isset($_POST['username']) && isset($_POST['password']))
{
function antiinjection($data)
{
$filter_sql = mysql_real_escape_string(stripslashes(strip_tags($data)));
return $filter_sql;
}
$username = antiinjection($_POST['username']);
$pass = antiinjection($_POST['password']);
$login = mysql_query("SELECT username, password FROM user WHERE (username='$username' OR email='$username') AND password='$pass'");
$r = mysql_fetch_array($login);
if((!empty($username)) && (!empty($pass)) && is_array($r))
{
if (count($r) > 0)
{
$_SESSION['username'] = $r['username'];
$_SESSION['password'] = $r['password'];
$date_log = date("j-F-Y, G:i");
mysql_query("UPDATE user SET status = 'online', date_logged_in = '$date_log' WHERE username = '$_SESSION[username]'");
header('Location: http://domen.com/');
}
else
{
echo '<div class="error_log">
<p>Wrong username or password. Please try again.</p>
</div>';
}
}
else
{
echo '
<div class="error_log">
<p>Username and password are required.</p>
</div>
';
}
} else {
// do some action
}