在主PHP文件中查看包含文件的PHP变量

I have a PHP file "main.php" that has at the top the following statement:

include "config_file.php";

The config_file.php includes the settings of five simple variables. Is there a way to display or view these five variables in the main.php file? If not, is there a better way to define these variables outside the main.php file (in a config file) and yet see the variables in the main.php file? An example will help.

Thanks, Menachem

index.php

include 'config_file.php';
if(isset($db))
    echo 'set';
else
    echo 'not set'; // this will be called

config_file.php

$db = new mysqli("HOST", "USERNAME", "PASSWORD", "DB");

And Possible duplicate of How to access variable from an included page?

Edit 01

a.php

$a = 'Abulla';
$b = 'Menachem';

b.php

you can just use

include 'a.php';
echo $a.' and '.$b;

You can directly use the variable of included file

just

echo $var;

Including the PHP file usually will give you access to all variables defined in this file. That means that you can simply use variables defined in config_file.php in your main.php.

Example:

Main.php:

 <?php
    include "config_file.php";
    // The code included below is example, you may do anything you want with variables
    $example_result = $a + $b;
print($example_result); // Just and example
    file_put_contents ("debug.txt" , $example_result); // Just an example
    // This should result in debug.txt contain $a + $b meaning that this file content should be "3"

config_file.php:

   <?php
 $a = 1;
 $b = 2;

This may slightly differ if one of your files is a PHP class. In this case please give us a notice.

The reason that I wanted to view the "include" file variables in the source code was to improve the readability of the code.

I solved this problem by pasting the content of the "include" file into the main file as comments.