pg_select Equivalent in libpq

Hi,

I am new to this list so if I ask a dump question please forgive me :)

I am writing a GTK+ C program using libpq.

At some point, I need to process each tuple returned by the PQexec
SELECT query as soon as it is received. (Actually I like to insert them
in a table widget).

But when I execute PQExec, all the SELECT result is fetched first. I
have a very big table so I need to insert each row as soon as they are
fetched from the server.

The pg_exec function does this but it is in TCL library.

How can I achive the same result in libpq?

Thanks for bearing me.

Ecmel