I suggest that you use libpqxx. libpqxx already has a utility template
function called separated_list() that lives in the pqxx namespace for
converting std containers into array literals. It also has a function
template called "from_string" that lives in the same place. I imagine
it's implemented in terms of stringstream though (otherwise, JTV would
have written a bunch of specialisations or overloads), and as such is
highly generic and unlikely to do what you want (I've just taken a
look at the doxygen generated docs on pqxx.org, I cannot confirm that
right now).
In any case, you are better of with pqxx. You can make some noise on
the pqxx mailing list if you feel that it ought to have this
functionality.
Regards,
Peter Geoghegan