PHP global declaration.

Question

I'm using PHP's global declaration to make an array available to a number of functions in a script. The variable is declared at the top of the script and is referenced with global in each of the functions which uses it, as follows:

<?php

$myarray = array(1, 2, 3);

function print_my_array() {
    global $myarray;

    print '<ul>';
    foreach($myarray as $entry) {
        print '<li>'.$entry.'</li>';
    }
    print '</ul>';  

    return 0;
}

print_my_array();

?>

Sometimes, but not always, the array is not set when the function is called, generating an error when the foreach is called. In the actual code, the array used is given a very unique name and so should not be causing any collisions with anything else. Am I mis-using the global declaration?

Answer 1

No, the snippet is correct. The problem you're having is the problem of using global variables – they can be accessed and changed from anywhere (perhaps accidental), thereby creating hard-to-find bugs.

Answer 2

The least you could do is check if the array is null at the top of the function, before you run the foreach. that would at least prevent the error:

function print_my_array() {
    global $myarray;

    if(!empty($myarray)) {
        print '<ul>';
        foreach($myarray as $entry) {
            print '<li>'.$entry.'</li>';
        }
        print '</ul>';  
    }
}

Also, I wouldn't just return 0 for the hell of it. You may want to incorporate whether or not the array was empty into what you return from this function.

Answer 3

By using globals you can hit quite a few gotchas, they'll also make you code less reusable.

Here's an example of your function which can be re-used many times across the site.

(untested)

<?php
function arrayTags($items, $open = '<li>', $close = '</li>')
{
    if (is_array($items) && count($items) != 0)
    {
        $output =   null;

        foreach ($items as $item) {
            $output .= $open . $item . $close;
        }

        return $output;
    }
    else
    {
        return '';
    }
}

// Default, <li>
echo '<ul>' . arrayTags($myarray) . '</ul>';

// or, spans:
echo '<div id="container">' . arrayTags($myarray, '<span>', '</span>') . '</div>';