Accessing Variables with the global Statement

From within one function, you cannot (by default) access a variable defined in another function or elsewhere in the script. Within a function, if you attempt to use a variable with the same name, you will only set or access a local variable. Let's put this to the test :

<?php

$life = 42;

function meaningOfLife() {

echo "The meaning of life is ".$life;

}

meaningOfLife();

?>

Put these lines into a text file called scopetest2.php and place this file in your web server document root. When you access this script through your web browser, it should look like:

As you might expect, the meaningOfLife() function does not have access to the $life variable in line 2; $life is empty when the function attempts to print it. On the whole, this is a good thing because it saves us from potential clashes between identically named variables, and a function can always demand an argument if it needs information about the outside world. Occasionally, you may want to access an important variable from within a function without passing it in as an argument. This is where the global statement comes into play. Use global to restore order to the universe.

<?php

$life=42;

function meaningOfLife() {

global $life;

echo "The meaning of life is ".$life;

}

meaningOfLife();

?>

Put these lines into a text file called scopetest3.php and place this file in your web server document root. When you access this script through your web browser, it should look like:

By placing the global statement in front of the $life variable when we declare it in the meaningOfLife() function (line 4), it now refers to the $life variable declared outside the function (line 2).

You will need to use the global statement within every function that needs to access a particular named global variable. Be careful, though; if you manipulate the contents of the variable within the function, the value of the variable will be changed for the script as a whole.

You can declare more than one variable at a time with the global statement by simply separating each of the variables you want to access with commas:

global $var1, $var2, $var3;

Watch Out!

Usually, an argument is a copy of whatever value is passed by the calling code; changing it in a function has no effect beyond the function block. Changing a global variable within a function, on the other hand, changes the original and not a copy. Use the global statement carefully.