Problem linkint with libpq

I'm trying to compile a small c program that integrates with PostgreSQL,
but when I get to link the prog i get the following error.

/tmp/ccFrRISc.o: In function `main':
/tmp/ccFrRISc.o(.text+0x57): undefined reference to `PQsetdbLogin'

I'm doing this on FreeBSD 4.3 and PostgreSQL is 7.1.2

I made this prog to determin that what causes the problem:

#include </usr/local/include/pgsql/libpq-fe.h>

int main (void) {
char *pghost,
*pgport,
*pgoptions,
*pgtty,
*dbUser,
*dbPassword;
char *dbName;
int nFields;
int i, j;
PGconn *conn;

pghost = "localhost";
pgport = "5432";
pgoptions = NULL;
pgtty = NULL;
dbName = "monitor";
dbUser = "username";
dbPassword = "donttell";

conn = PQsetdbLogin(pghost, pgport, pgoptions, pgtty, dbName, dbUser,
dbPassword);
return(0);
}

\Flemming