'White Screen of Death' Causes - WordPress CMS

Question

I have recently installed a theme on WordPress and when activated it merely results in a blank white screen. What are the possible causes of this? and the steps in which to take to start finding the issue.

The problem revealed itself when moving the site from our test server to the hosting company's sever, which we have used to host various other WordPress sites. What are the likely causes of white screen in my instance? and the steps in which to take to start finding the issue. I have took steps following research such as increasing memory limit and disabling plugins etc but they worked fine on the original server so I doubt it can be caused by plugins etc.

Thank you

UPDATE

Right, so far, I have increased the memory limit to 128M, and disabled all plugins as well as temporarily naming their folders.

I have enabled to debugging thanks to the suggestion by @Sabari, this has resulted in the following error: Fatal error: Call to undefined function mb_internal_encoding() in /home/neatly/public_html/wp-content/themes/best_wedding_dress-babe23c7e828662f1a07c296a5608f52/functions.php on line 12

I am less than useless with PHP but you could make some suggestions on how to proceed that would be excellent such as where and how to define mb_internal_encoding. Here is the code on line 12:

mb_internal_encoding(get_bloginfo('charset'));

I would like to reiterate that this worked perfectly on our test server and all these issues only developed when moved to a new server. I have transferred WordPress sites from one server to another many times and have re-downloaded and uploaded both the content and database three times on this specific website. Both versions (test server and new server) have the same versions of WordPress so it could be possibly that the new server has different technology. Is there anything along these lines that could be causing this error?

Answer suggested by Sabari

The issue was solved by enabling and configuring mbstring (multibyte support) on our webhost's server.

Answer 1

WSOD. OK... possible cause, theme exhausts the memory limit
a) clear you cache
b) Make a backup before changing anything
c) Disable the plugins,  
d) Replace Theme with a Default Theme
e) Re-install Wordpress

use debugging for troubleshooting

error_reporting(E_ALL); ini_set('display_errors', 1);

In Wordpress:

define( 'WP_DEBUG', true);

Answer 2

I think your issue is regarding with mbstring extension not enabled.

mb_internal_encoding function requires mbstring extension . It is a non-default extension, that is not enabled by default.

You can see this for more info on how to install and configure mb_string http://www.php.net/mbstring.

If you are on windows then uncomment the line (remove semicolon before extension=php_mbstring.dll) extension=php_mbstring.dll; in php.ini.

If you are on linux you could try yum install php-mbstring for centos.

For ubuntu I am not clear.

Restart apache after this.

UPDATE :

To check if extension is enabeled you can use :

if (extension_loaded('mbstring')) {
    //functions using mb string extensions
}

NEW UPDATE :

if (extension_loaded('mbstring')) {
    mb_internal_encoding(get_bloginfo('charset'));
}

I think WordPress has a built in function wp_set_internal_encoding() which will handle these. You just need to call this function in your file. What wp_set_internal_encoding() does is the same thing I explained above :

function wp_set_internal_encoding() {
    if ( function_exists( 'mb_internal_encoding' ) ) {
        if ( !@mb_internal_encoding( get_option( 'blog_charset' ) ) )
            mb_internal_encoding( 'UTF-8' );
    }
}

It checks whether the mb_internal_encoding function exists (the function will only exist if the extension is loaded). This is another way to check if the function exists.

The advantage will be that you have to call only the function and don't worry about the other things. WordPress will handle those .

NEW UPDATE :

For your first error, wrap your mb_strlen function inside the function_exists () like :

if ( function_exists( 'mb_strlen' ) ) {
    mb_strlen();
 }

May be if you have the extension enabled and it may have been corrupted. So it is better to check if the function exists before calling that .

For your second error, you don't need to add the wp_set_internal_encoding in your functions.php or any other file. It is a WordPress inbuilt function. You just need to call the function wp_set_internal_encoding. You are actually declaring the function which exists. So PHP will return fatal error.

NEW UPDATE

In your function you have mb_strlen which will work only mbstring extension is enabled. So you should change

function theme_trim_long_str($str, $len = 50, $sep = ' '){
    $words = split($sep, $str);
    $wcount = count($words);
    while( $wcount > 0 && mb_strlen(join($sep, array_slice($words, 0, $wcount))) > $len)     $wcount--;
    if ($wcount != count($words)) {
        $str = join($sep, array_slice($words, 0, $wcount)) . '…';
    }
    return $str;
}

to

function theme_trim_long_str($str, $len = 50, $sep = ' '){
    $words = split($sep, $str);
    $wcount = count($words);

    if ( function_exists( 'mb_strlen' ) ) {
        while( $wcount > 0 && mb_strlen(join($sep, array_slice($words, 0, $wcount))) > $len)     
            $wcount--;
    } else {
        while( $wcount > 0 && strlen(join($sep, array_slice($words, 0, $wcount))) > $len)
            $wcount--;
    }
    if ($wcount != count($words)) {
        $str = join($sep, array_slice($words, 0, $wcount)) . '…';
    }
    return $str;
} 

Hope this helps you :)

Answer 3

Many things can happen. If files are not uploaded properly, then it may happen. If the theme has any error with function file, also then it may happen.