When using Advanced Custom Fields in WordPress, I often get and use a custom link field like this:

<?php
$link = get_field( 'link' );
$link_url = $link['url'];
?>

When doing this, PHP will gently remind me with a notice that I have used an illegal string offset.

Warning: Illegal string offset ‘url’…

The top result in Google send us to this ACF support page. I usually figure out the problem right away with these support links, but this one was a little difficult for me to follow, as it winds through some different possibilities, including a plugin conflict.

The answer lies within the responses, though: “the field is returning false.” I often use ACF to check if a value is present on a page. If it is, something happens. The field return false if the field is NOT present on the page. That means the conditional is not true and PHP 7.1 considers this illegal for using a variable array.

The solution is really simple and is the standard way of testing to see if the value is true or false: using a conditional.

<?php 
$link = get_field( 'link' );
if ( $link) :
$link_url = $link[ 'url' ];
endif;
?>

The code added was “if ( $link ) :” and it’s ending statement “endif;”.

Here’s the ACF Link documentation for reference.

This note is mostly so I can get to the answer quickly and learn it more deeply myself, but I hope it helps you if happen across it, too.