trying to connect to PostgreSQL

I'm a relative newcomer to PostgreSQL. I read the page on its website
that explained how to connect, and I tried to compile the following
example program. I located a "libpq-fe.h" at "/usr/include/pgsql" so
I executed the command:

cc -o pgsConnect -I/usr/include/pgsql pgsConnect.c

I got a whole bunch of error messages listing a whole bunches of oc-
currences of an "undefined reference to" some C function. I went
through my local copy of "libpq-fe.h" and found references to each of
those functions, but they were all declared "extern". Do I have to
actually have those functions defined somewhere in order to get this
code to compile? If so, how can I get them defined?

The offending references were:

PQstatus PQerrorMessage PQexec PQresultStatus
PQclear PQnfields PQfname PQgetvalue
PQntuples PQfinish

And the code I used was:

/*
* testlibpq.c
*
* Test the C version of libpq, the PostgreSQL frontend library.
*/
#include <stdio.h>
#include <stdlib.h>
#include "libpq-fe.h"

static void
exit_nicely(PGconn *conn)
{
PQfinish(conn);
exit(1);
}

int
main(int argc, char **argv)
{
const char *conninfo;
PGconn *conn;
PGresult *res;
int nFields;
int i,
j;

/*
* If the user supplies a parameter on the command line, use it as the
* conninfo string; otherwise default to setting dbname=postgres and using
* environment variables or defaults for all other connection parameters.
*/
if (argc > 1)
conninfo = argv[1];
else
conninfo = "dbname = postgres";

/* Make a connection to the database */
conn = PQconnectdb(conninfo);

/* Check to see that the backend connection was successfully made */
if (PQstatus(conn) != CONNECTION_OK)
{
fprintf(stderr, "Connection to database failed: %s",
PQerrorMessage(conn));
exit_nicely(conn);
}

/*
* Our test case here involves using a cursor, for which we must be inside
* a transaction block. We could do the whole thing with a single
* PQexec() of "select * from pg_database", but that's too trivial to make
* a good example.
*/

/* Start a transaction block */
res = PQexec(conn, "BEGIN");
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "BEGIN command failed: %s", PQerrorMessage(conn));
PQclear(res);
exit_nicely(conn);
}

/*
* Should PQclear PGresult whenever it is no longer needed to avoid memory
* leaks
*/
PQclear(res);

/*
* Fetch rows from pg_database, the system catalog of databases
*/
res = PQexec(conn, "DECLARE myportal CURSOR FOR select * from
pg_database");
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "DECLARE CURSOR failed: %s", PQerrorMessage(conn));
PQclear(res);
exit_nicely(conn);
}
PQclear(res);

res = PQexec(conn, "FETCH ALL in myportal");
if (PQresultStatus(res) != PGRES_TUPLES_OK)
{
fprintf(stderr, "FETCH ALL failed: %s", PQerrorMessage(conn));
PQclear(res);
exit_nicely(conn);
}

/* first, print out the attribute names */
nFields = PQnfields(res);
for (i = 0; i < nFields; i++)
{ printf("%-15s", PQfname(res, i));
}
printf("\n\n");

/* next, print out the rows */
for (i = 0; i < PQntuples(res); i++)
{
for (j = 0; j < nFields; j++)
{ printf("%-15s", PQgetvalue(res, i, j));
}
printf("\n");
}

PQclear(res);

/* close the portal ... we don't bother to check for errors ... */
res = PQexec(conn, "CLOSE myportal");
PQclear(res);

/* end the transaction */
res = PQexec(conn, "END");
PQclear(res);

/* close the connection to the database and cleanup */
PQfinish(conn);

return 0;
}

---Kevin Simonson

"You'll never get to heaven, or even to LA,
if you don't believe there's a way."
from _Why Not_