How to display the buyer's name on the header in Opencart?

Question

opencart

Good afternoon, gentlemen,
I was given the task to display the name and surname of an authorized user in a certain place on the header. I googled and many times. Found different ways, tried them and nothing worked.
I in one of the solutions it was said like this:
In the header.php in the folder along the path opencart/catalog/controller/common/ and add the lines:

$data['firstname'] = $this->customer->getFirstName();
      $data['lastname'] = $this->customer->getLastName();

And in header.tpl along the path opencart/catalog/view/theme/mytheme/template/common/

<?php echo $firstname; ?>
      <?php echo $lastname; ?>

That's exactly what I did. The server responds that the variables are undefined. Maybe these lines need to be written somewhere else.
Please advise gentlemen.

Answer 1

check first in the controller whether the variables are defined or not
above this line
$data['firstname'] = $this->customer->getFirstName();
to be sure, check also $this->customer->getId()
write down

echo $this->customer->isLogged()."-".$this->customer->getId()."-".$this->customer->getFirstName()."-".$this->customer->getLastName(); exit;

more than sure that it will give out emptiness, most likely you are checking without logging in as a buyer.
I would write in the controller like this to be sure

if ($this->customer->isLogged()) {
$data['firstname'] = $this->customer->getFirstName();
$data['lastname'] = $this->customer->getLastName();
} else {
$data['firstname'] = '';
$data['lastname'] = '';
}