determining an endpoint's family - endpoint_type/protocol_type?

I am developing an FTP client with boost::asio, and I wish to
determine whether an endpoint (generated by a resolver) is IPv4 or
IPv6.

The only way I can see how is to compare endpoint.protocol().family()
with AF_INET and AF_INET6, which doesn't feel like the right way. An
alternative would be to specify the desired family before the host is
resolved, or to simply compare the endpoint's family against some
predefined boost::asio::ip::ipv6/ipv4 members.

The difference between IPv4 and IPv6 is quite significant for FTP, as
they require a different set of (mostly incompatible) commands to
negotiate data connections.

Any suggestions? (Probably I have missed something :)

Richard

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