cannot start session when headers already sent-CodePudding

Im getting following error in live server, when user login, is sent to dashboard.

warning:session_start():cannot start session when headers already sent in … on line 3

warning:cannot modify header information-header already sent by(output started at…)in…on line 5

<?php
ob_start();
session_start();
?>
<?php
if(isset($_POST['login'])){
    $username = $_POST['username'];
    $password = $_POST['password'];
    try {
        $data = $conn->prepare("SELECT * FROM users WHERE username = :username");
        $data->bindParam(':username', $username, PDO::PARAM_STR); 
        $data->execute();
    } catch (PDOException $e) {
        $e->getMessage();
        die("Something went wrong please contact your adminstrator");
    }
     while($rows = $data->fetch(PDO::FETCH_OBJ) ){
       $user_id = $rows->user_id;
       $db_username = $rows->username;
       $db_password = $rows->password;
       $db_user_role = $rows->user_role;
       $db_user_image = $rows->user_image;
     }
     $verifyPassword = password_verify($password, $db_password );
     if($username === $db_username && $verifyPassword){
        $_SESSION['username'] = $db_username;
        $_SESSION['user_role'] =  $db_user_role;
        $_SESSION['user_image'] =  $db_user_image;
        $_SESSION['message'] = '';
        $_SESSION['IS_LOGIN']='yes';

        header('Location:admin');
    }else{
        //header('Location:index.php');
        echo "<script>alert('Invalid Paswword')</script>";
    }
}
?>

After successful login its redirect to dashboard im getting error in this page.

warning:session_start():cannot start session when headers already sent in … on line 3

warning:cannot modify header information-header already sent by(output started at…)in…on line 5

<?php
ob_start();
session_start();//line 3
if(!isset($_SESSION['user_role'])){
header('Location:../index.php');//line 5
}
?>
<!DOCTYPE html>
<html lang="en">
<head>

CodePudding user response：

header() always has to be the first thing on your page:

<html></html>
<?php header('location: xy'); ?>

Output:

Warning: Cannot modify header information - headers already sent by (output started at /home/user/scripts/code.php:1) in /home/user/scripts/code.php on line 2

Instead:

<?php header('location: xy'); ?>
<html></html>

Throws no error

So either you have to use header() at the top or you have to use pure html for the redirect:

<meta http-equiv="refresh" content="0; url=http://example.com/" />

CodePudding user response：

If your php version PHP >= 5.4.0 , PHP 7, PHP 8

if (session_status() === PHP_SESSION_NONE) {
    session_start();
}

else PHP < 5.4.0

if(session_id() == '') {
    session_start();
}

If it is work/does not work give me feedback so I will try another way.