How to redirect to another page using PHP

Question

I have been building a website which includes a login page. I need to redirect the user to their profile page once they've logged in successfully, but I don't know how to do that in PHP as this is my first website. I've searched the internet and have been told that the header() function should do the trick, but it will only work if I haven't output any information before using it.

The problem is that I've outputted a bunch of information Including the HTML to build the login page itself. So how do I redirect the user from one page to the next?

What options do I have? Also, what is the best practice in these instances?

EDIT: Here's my entire login.php page:

<?php 

session_start(); 

echo "<!DOCTYPE html> 
      <html> 
                <head> 
                        <meta charset='utf-8'> 
                        <title>Sprout</title> 
              <link rel='stylesheet' href='stylesheet.css' type='text/css'> 
                  </head> 
      <body> 
              <div class='box'> 
            <form action='login.php' method='post'> 
            Name<br /> <input type='text' name='username' class='form'/><br /> 
            Password<br /> 
            <input type='password' name='password' class='form'/> <input type='submit' value='Login' class='button' /> 
            </form> 
          </div> 
        </body> 
</html>"; 

if ($_SERVER['REQUEST_METHOD'] == 'POST') 
{ 


$username = $_POST["username"]; 
$password = $_POST["password"]; 

$dbhost = "localhost"; 
$dbuser = "root"; 
$dbpass = "root"; 

$conn = mysql_connect($dbhost, $dbuser, $dbpass) or die ("Error connecting to database"); 

$dbname = "database"; 

mysql_select_db($dbname); 

$query = "SELECT username FROM users WHERE username = '$username' AND password = '$password'"; 

$result = mysql_query($query) or die ("Failed Query of " . $query); 

while($row = mysql_fetch_assoc($result)) 
{ 

                $_SESSION["user"] = $username; 
          } 
} 
?>

Aditya · Answer 1 · Feb 18, 2022

You could use a function which is similar to:

function redirect($url) { 
            ob_start(); 
            header('Location: '.$url); 
            ob_end_flush(); 
            die(); 
}

A user should always remember that you should always use either ob_flush() or ob_start() at the beginning of your header('location: ...'); functions, and you should always follow them with a die() or exit() function to prevent further code execution.

Therefore, using die() / exit() functions in your redirects, as well as when to use ob_flush() vs ob_start() will help you get the answer to your problem.