当变量不存在时，如何在php中避免未定义的变量？

Question

I only touch php on the very basic stuff.

But I always like to avoid errors/notices when making wordpress themes.

I have a simple function below that I made to list my taxonomy terms.

$tax = 'dealer-communications';
$terms = get_terms($tax);
$count = count($terms);
if ( $count > 0 ){
    echo '<li class="nav-header">Dealer communications</li>';
    foreach ( $terms as $term ) {
        if (get_queried_object()->slug == $term->slug) $active = 'class="active"';
        echo '<li '.$active.'><a href="'.get_term_link($term->slug, $tax).'">' . $term->name . '</a></li>';
    }
}

As you can see I have a $active variable.

This active variable is undefined when the my get_queried_object()->slug does not match $term->slug

How can I avoid my active variable from being undefined. So it is defined but empty.

They only way my brain could work it out is by doing this...

$active = null;
if (get_queried_object()->slug == $term->slug) $active = 'class="active"';

or...

if (get_queried_object()->slug == $term->slug) {
    $active = 'class="active"';
} else {
    $active = '';
}

Is this the most efficient way of doing this or is there an alternative php method?

Many Thanks Josh

Answer 1

There is no alternative php method, but for readability you should not declare/init your variables in a if block, e.g. :

foreach ( $terms as $term ) {
    $active = '';
    if (get_queried_object()->slug == $term->slug) $active = 'class="active"';
    echo '<li '.$active.'><a href="'.get_term_link($term->slug, $tax).'">' . $term->name . '</a></li>';
}

You can also use ternary operator (but not really readable) :

$active = (get_queried_object()->slug == $term->slug) ? 'class="active"' : '';