Fatal error: Call to undefined function add_filter() in index.php in Wordpress

Question

I want to change my wordpress theme dynamically by user browser. So I found this code on the net and added it to my index.php file

add_filter('template', 'switch_theme_by_browser');
add_filter('stylesheet', 'switch_theme_by_browser');

function switch_theme_by_browser($theme) {

    $browser = $_SERVER['HTTP_USER_AGENT'];

    if(preg_match('/MSIE/i',$browser) && !preg_match('/Opera/i',$browser))
    {
        $theme = "twentyeleven";
    }
    elseif(preg_match('/Firefox/i',$browser))
    {
        $theme = "twentyten";
    }
    elseif(preg_match('/Chrome/i',$browser))
    {
        $theme = "Boxoffice";
    }

    return $theme;
}

After that it shows me "Fatal error: Call to undefined function add_filter() in /home/xxx/public_html/domain.com/index.php on line 17"

As I undertand the "add_filter()" should be a function that is built in wordpress.

The thing is, it should be the very first thing to be read by the site so it knows what template to load up. — Karuvägistaja
– Karuvägistaja, Commented Nov 7, 2012 at 22:37

Michael Lewis · Accepted Answer · 2012-11-07 21:50:47Z

0

As Dawson said, this needs to go in your /wp-content/themes/[theme]/functions.php file.

answered Nov 7, 2012 at 21:50

Michael Lewis

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1 Comment

Karuvägistaja Over a year ago

ok, now it says:Warning: require(/home/xxx/public_html/domain.net/wp-content/themes/twentyten/inc/theme-options.php) [function.require]: failed to open stream: No such file or directory in /home/xxx/public_html/domain.net/wp-content/themes/twentyeleven/functions.php on line 122 Fatal error: require() [function.require]: Failed opening required '/home/xxx/public_html/domain.net/wp-content/themes/twentyten/inc/theme-options.php' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home/xxx/public_html/domain.net/wp-content/themes/twentyeleven/functions.php on line 122

zzxwill · Accepted Answer · 2014-04-12 03:07:30Z

0

In wordpress root directory, put require( ABSPATH . WPINC . '/plugin.php' ); before require( ABSPATH . WPINC . '/functions.php' ); in file wp-settings.php. I verified this solution at http://wordpress.org/support/topic/fatal-error-call-to-undefined-function-add_filter.

answered Apr 12, 2014 at 3:07

zzxwill

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