(PHP 4, PHP 5)
gethostbyname — Get the IPv4 address corresponding to a given Internet host name
$hostname
   )
   Returns the IPv4 address of the Internet host specified by
   hostname.
  
hostnameThe host name.
   Returns the IPv4 address or a string containing the unmodified
   hostname on failure.
  
Example #1 A simple gethostbyname() example
<?php
$ip = gethostbyname('www.example.com');
echo $ip;
?>