ErcanOPAK.com

After upgrading  to  PHP 7.x from PHP 5.x, you start getting  error of “Call to undefined”.

This is because mysql_* functions are completely removed from PHP 7, it was get deprecated in PHP 5.5 but now it is completely removed.

The older mysql function are removed due to following reasons:

1. Not work on Object Oriented concept
2. Not support transactions and prepared statements
3. Insecure

Here is how you can connect to MySQL with MySqli connection object:

<?php

$conn = mysqli_connect("localhost", "username", "password", "database");

?>

or more detailed:

<?php

try 
{
    $conn = mysqli_connect("localhost", "username", "password") or die("Error: " . $mysqli_connect_error());
    $db = mysqli_select_db($conn, "database");
} 
catch (Exception $e) 
{
    die("Unexpected Error: " . $e->getMessage());
}

?>

So, before you upgrade to PHP 7.x, first you must update your code.