"Fatal error: Cannot redeclare <function>"

This errors says your function is already defined ; which can mean :

• you have the same function defined in two files
• or you have the same function defined in two places in the same file
• or the file in which your function is defined is included two times (so, it seems the function is defined two times)

To help with the third point, a solution would be to use include_once instead of include when including your functions.php file -- so it cannot be included more than once.

You're probably including the file functions.php more than once.

Solution 1

Don't declare function inside a loop (like foreach, for, while...) ! Declare before them.

Solution 2

You should include that file (wherein that function exists) only once. So,
instead of :  include ("functions.php");
use:             include_once("functions.php");

Solution 3

If none of above helps, before function declaration, add a check to avoid re-declaration:

if (!function_exists('your_function_name'))   {
  function your_function_name()  {
    ........
  }
}

You can check first whether the name of your function exists or not before you declare the function:

if (!function_exists('generate_salt'))
{
    function generate_salt()
    {
    ........
    }
}

OR you can change the name of the function to another name.