When installing WordPress MU (WPMU), an administrator can choose to use sub-domains or sub-directories for blog addresses. This presents a challenge for WordPress Plugin and Theme developers. How can a Plugin of Theme function determine if WordPress MU is using sub-domains or sub-directories?
The VHOST constant stores whether WordPress MU is using sub-domains for blog addresses. If an administrator chooses to use sub-domains, VHOST contains a value of "yes". If the administrator chooses to use sub-directories, VHOST is set with a value of "no".
A WordPress Plugin or Theme function can access the value of VHOST using the PHP constant function.
<?php constant( "VHOST" ); ?>
The VHOST constant could be used within a plugin to control a logical test. The code below will print a different message depending on whether WPMU is using sub-domains or sub-directories.
if( constant( "VHOST" ) == 'yes' )
echo "I'm using sub-domains for blog addresses!";
else
echo "I'm using sub-folders for blog addresses.";
For more information on the PHP Constant VHOST used in WordPress MU, see: