PHP 7.2 - Include file cannot access another include file - php

Question

I am having an issue with an include file accessing another include file (my db connection)
I have a site with the following layout ::
root/conn.php :: db connection file
root/site/file1.php :: regular page
root/site/include/func.inc :: file with functions in it
Each file is listed below with appropriate code...
conn.php ::
<?php
$host = 'localhost';
$db = 'mydb';
$user = 'myuser';
$pass = 'mypass';
$charset = 'utf8mb4';
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
try {
$conn = new mysqli($host, $user, $pass, $db);
$conn->set_charset($charset);
} catch (\mysqli_sql_exception $e) {
throw new \mysqli_sql_exception($e->getMessage(), $e->getCode());
}
unset($host, $db, $user, $pass, $charset);
?>
file1.php ::
include_once ("{$_SERVER['DOCUMENT_ROOT']}/conn.php");
include_once ("{$_SERVER['DOCUMENT_ROOT']}/site/include/func.inc");
{ code that calls functions in func.php }
func.inc ::
include_once ("{$_SERVER['DOCUMENT_ROOT']}/conn.php");
{ various functions }
When I browse to /file1.php, I get the following error ::
PHP Notice: Undefined variable: conn in C:\inetpub\root\site\include\func.inc on line 231
PHP Fatal error: Uncaught Error: Call to a member function prepare() on null in C:\inetpub\root\site\include\func.inc:231
my func.inc file cannot seem to find the conn.php file. I have also tried removing the include function from func.inc. There are other files in the /include folder that can access the conn.php file with the same include function.

Answer 1

The issue relates to something called the variable scope (https://www.php.net/manual/en/language.variables.scope.php)
==> Please read that to get detailed information
The second example describes your problem
func.inc
<?php
include_once ("{$_SERVER['DOCUMENT_ROOT']}/conn.php");
// to illustrate the issue, the include can be simplified to
// $conn = "something"; // => global scope variable
function myFunc(){
echo $conn; //no output - $conn exists ONLY in the local scope --> not available inside thisfunction
}
Solution 1:
func.inc
<?php
function myFunc($conn){
echo $conn; //outputs $conn
}
file1.php
<?php
include_once ("{$_SERVER['DOCUMENT_ROOT']}/conn.php");
include_once ("{$_SERVER['DOCUMENT_ROOT']}/site/include/func.inc");
//call function and pass the $conn, it's available here in the global scope
myFunc($conn);
Solution 2
but keep in mind global is considered as bad practice
func.inc
<?php
include_once ("{$_SERVER['DOCUMENT_ROOT']}/conn.php");
function myFunc(){
global $conn; //$conn is declared global in the local scope of this function
echo $conn; //outputs $conn from conn.php if you call myFunc from anywhere
}