Help with pq++

Hello
I need to make a program that uses pq++, before starting I made a little program to see if I understood correctly how
touse pq++, however I have a problem: The program can't connect to the DB. 
My code looks like this:
#include <stdio.h>
#include <libpq++.h>

int main()
{
   PgDatabase db("dbname=mydb");
   if (!(db.ConnectionBad()))
   {
      printf("OK\n");
      exit(0);
   }
   else
   {
      printf("Error connecting\n");
      exit(1);
   }
}

And no matter what I do (I tried with the env variables PGHOST, PGPORT, PGDATABASE and PGUSER) the program always gives
me"Error connecting". 
Can somebody help? I was expecting to have problems, but not this early.

Aristide