connecting to a remote pq always require a password

Hi,

I am trying to use the libpq to connect to my postgresql 8.3 server.
If I use "dbname = mydb", the connection made successfully because I
am using a socket connection. But if I use "host = 127.0.0.1 dbname =
mydb", the error message is "no password supplied".

In the pg_hba.conf file, I even change the host access control to this:
host all all 127.0.0.1/32 trust

but it still does not work. What I missed?

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Best Regards,
David Shen