(p.s. UPDATE : this method doesnt work correctly at this moment)
When your hosting doesnt support WildCard subdomains, you can use this method:
Manually create this file /subdomain/index.php with this content:
<?php require_once( __dir__ . '/../index.php' ); ?>
and /subdomain/wp-admin/index.php with this content:
<?php require_once( __dir__ . '/../wp-admin/index.php' ); ?>
and /subdomain/.htaccess with this content (just change example.com ):
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*?)$ http://example.com/$1 [L,R] RewriteBase / RewriteRule ^index\.php$ - [L] # add a trailing slash to /wp-admin RewriteRule ^wp-admin$ wp-admin/ [R=301,L] RewriteCond %{REQUEST_FILENAME} -f [OR] RewriteCond %{REQUEST_FILENAME} -d RewriteRule ^ - [L] RewriteRule ^(wp-(content|admin|includes).*) $1 [L] RewriteRule ^(.*\.php)$ $1 [L] RewriteRule . index.php [L] </IfModule>
Note, that the only drawback of this code, is that it redirects all urls (not found files at subdomain) to root domain url, instead of rewriting.. I mean, if you visit subdomain.example.com/myfile.jpg it redirects to example.com/myfile.jpg.