(PHP 4 >= 4.3.0, PHP 5)
socket_set_option — Sets socket options for the socket
   The socket_set_option() function sets the option
   specified by the optname parameter, at the
   specified protocol level, to the value pointed to
   by the optval parameter for the 
   socket.
  
socketA valid socket resource created with socket_create() or socket_accept().
level
       The level parameter specifies the protocol
       level at which the option resides. For example, to retrieve options at
       the socket level, a level parameter of
       SOL_SOCKET would be used. Other levels, such as
       TCP, can be used by specifying the protocol number of that level. 
       Protocol numbers can be found by using the 
       getprotobyname() function.
      
optnameThe available socket options are the same as those for the socket_get_option() function.
optvalThe option value.
   Returns TRUE on success or FALSE on failure.
  
Example #1 socket_set_option() example
<?php
$socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
if (!is_resource($socket)) {
    echo 'Unable to create socket: '. socket_strerror(socket_last_error()) . PHP_EOL;
}
if (!socket_set_option($socket, SOL_SOCKET, SO_REUSEADDR, 1)) {
    echo 'Unable to set option on socket: '. socket_strerror(socket_last_error()) . PHP_EOL;
}
if (!socket_bind($socket, '127.0.0.1', 1223)) {
    echo 'Unable to bind socket: '. socket_strerror(socket_last_error()) . PHP_EOL;
}
$rval = socket_get_option($socket, SOL_SOCKET, SO_REUSEADDR);
if ($rval === false) {
    echo 'Unable to get socket option: '. socket_strerror(socket_last_error()) . PHP_EOL;
} else if ($rval !== 0) {
    echo 'SO_REUSEADDR is set on socket !' . PHP_EOL;
}
?>