Passing a variable from one php include file to another: global vs. not

Question

I'm trying to pass a variable from one include file to another. This is NOT working unless I declare the variable as global in the second include file. However, I do NOT need to declare it as global in the file that is calling the first include. For example:

---

front.inc:

$name = 'james';

---

index.php:

include('front.inc');
echo $name;
include('end.inc');

output: james

---

end.inc:

echo $name;

output: nothing

---

IF I declare global $name prior to echoing $name in end.inc, then it works properly. The accepted answer to this post explains that this depends on your server configuration: Passing variables in PHP from one file to another

I'm using an Apache server. How would I configure it so that declaring $name to be global is not necessary? Are there advantages/disadvantages to one vs. the other?

Answer 1

The parent file has access to variables in both included files

When including files in PHP, it acts like the code exists within the file they are being included from. Imagine copy and pasting the code from within each of your included files directly into your index.php. That is how PHP works with includes.

So, in your example, since you've set a variable called $name in your front.inc file, and then included both front.inc and end.inc in your index.php, you will be able to echo the variable $name anywhere after the include of front.inc within your index.php. Again, PHP processes your index.php as if the code from the two files you are including are part of the file.

The included file doesn't have access to the other included file

When you place an echo within an included file, to a variable that is not defined within itself, you're not going to get a result because it is treated separately then any other included file.

In other words, to do the behavior you're expecting, you will need to define it as a global.

Answer 2

Here is a pitfall to avoid. In case you need to access your variable $name within a function, you need to say "global $name;" at the beginning of that function. You need to repeat this for each function in the same file.

include('front.inc');
global $name;

function foo() {
  echo $name;
}

function bar() {
  echo $name;
}

foo();
bar();

will only show errors. The correct way to do that would be:

include('front.inc');

function foo() {
  global $name;
  echo $name;
}

function bar() {
  global $name;
  echo $name;
}

foo();
bar();

Answer 3

Same here with php 5.4.7

$mysql = false;
include("inc_mysql.php");
echo($mysql);

Where inc_mysql.php:

$mysql = true;

Echoes a value of $mysql = false;

BUT

if you remove the first $mysql=false;

include("inc_mysql.php");
echo($mysql);

Echoes a value of $mysql = true;

SO definitively, doing an include IS NOT like copying/pasting code, at least, in some PHP versions.

Answer 4

This is all you have to do:

In front.inc

global $name;
$name = 'james';

Answer 5

It's all about scope. It seems that in PHP the variables defined in the global scope are not automatically inherited in the function's scope. That's why, within a function body, you have to prepend the variable with the global keyword.

From the PHP manual:

A true global variable imported inside a function scope with the global statement actually creates a reference to the global variable.

So the variable $name is available to both includes (front.inc and end.inc ) but any function defined in those files would not have access to variable $name unless the global keyword is used or the $GLOBALS constant.

I've grabbed some code from https://www.php.net/manual/en/language.variables.scope.php to better understand this issue:

<?php
$a = 1; /* global scope */ 

function test()
{
    /* the code below will throw a Warning: Undefined variable $a ... */
    echo $a; /* reference to local scope variable */
} 

To get the variable value you'll have to call global $a like this:

<?php
$a = 2; /* global scope */

function test2() {
    global $a;
    /* now we have access to the global $a so no more warnings */
    echo $a;
}

You can also rely on $GLOBALS to get access to the global like this:

<?php
$a = 3; /* global scope */

function test3() {
    echo $GLOBALS['a'];
}

You can get a list of all global variables with a code like this:

echo "<pre>";
print_r($GLOBALS);
echo "</pre>";

Source for code above: Is it possible to List Out All the Global variables in PHP?