wp_redirect() is not working

Question

My code is like below.

$result = $wpdb->query($sql);
if ( $result ) {
  wp_redirect( "http://www.example.com/contact-us");
  exit();
}

I am getting below error

Warning: Cannot modify header information - headers already sent by (output started at /var/www/html/wordpressplugin/wp-admin/includes/misc.php:1281) in /var/www/html/wordpressplugin/wp-includes/pluggable.php on line 1296

I tried with below code but I didn't get any solution

$result = $wpdb->query($sql);
if ( $result ) {
  ob_start();
  wp_redirect( "http://www.example.com/contact-us");
  ob_end_flush();
  exit();
}

Answer 1

Add ob_start(); at the top of functions.php file and remove from your code. As WP is a combination of plugin and core files and we don't know which code sends the throws the header sent warning. And we know that functions.php is called every time we made a request to server, so this is the ideal place to add the ob_start() code to overcome the problem.