With PHP 7.1, some PHP web applications fail because of deprecated code usage. This may result in an error message like [] operator not supported for strings for various Joomla!, WordPress and Drupal components. Here’s how to fix this code for PHP 7.1+.

I’ll use Joomla! as an example in this short post. The same error and fix may apply for other CMS systems like WordPress and Drupal.

First you have to enable Joomla! Debug modus, that’ll show you where the error is happening. Open up configuration.php and set public $debug to 1.

If you refresh the page now, you’ll see Joomla’s error page, telling you about Fatal error: Uncaught Error:

Fatal error: Uncaught Error: [] operator not supported for strings
D:\www\example.com\www\components\com_layer_slider\base\includes\slider_markup_init.php:98

OK, so we now know where the error is, it’s on line 98 in com_layer_slider’s base\includes\slider_markup_init.php file. In this case, the failing code is:

$data[] = '<script type="text/javascript">' . NL;

You can fix this PHP error by first initializing $data[] as an array:

$data = [];
$data[] = '<script type="text/javascript">' . NL;

A second method is to use the older style using array():

$data = array();
$data[] = '<script type="text/javascript">' . NL;

Let’s hope not too many Joomla! components, plugins and extensions use code like this. Not to mention other CMS systems like Expression Engine, WordPress, BuddyPress, PrestaShop…

Update 3-3-2018:
WordPress premium Betheme theme by Muffin group needs a fix in the file

wp-content\themes\betheme\functions\builder\front.php

On line 150:

// $section_style         = '';
$section_style         = [];

WordPress Revolution Slider
Older versions of Revolution Slider plugin by ThemePunch has this same deprecated PHP code, and throws an error:

Uncaught Error: [] operator not supported for strings in wp-content\plugins\revslider\includes\framework\base-admin.class.php:69

To fix this, add a line before line 69:

self::$arrMetaBoxes = []; # add this line to create the variable as an array
self::$arrMetaBoxes[] = $box;