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 to use 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