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C interface

From: Mario Fernandez <mfernandez(at)sia(dot)es>
To: "'pgsql-ports(at)postgresql(dot)org'" <pgsql-ports(at)postgresql(dot)org>
Subject: C interface
Date: 2001-08-20 17:36:38
Message-ID: 2DA55CB79DF6D411BAB500508BEA1F17055164@MAILSRV (view raw or flat)
Thread:
Lists: pgsql-ports
I´ve got a problem when trying to access Postgresql through C language. I´ve
copied the first example appearing in the integrated docs documentation( for
version 7.0.x). The example is the one beloww, but when I compile it I get
two problems:

Firstly, the include file "libpq-fe.h" wasn´t found. I fixed it writing the
absolute path in the #include.

Secondly, when that one was found, there were a lot of 'undefined
references' to every function in testlibpq.c. The output is the following:

/tmp/ccIKrZnW.o: In function `exit_nicely':
/tmp/ccIKrZnW.o(.text+0xe): undefined reference to `PQfinish'
/tmp/ccIKrZnW.o: In function `main':
/tmp/ccIKrZnW.o(.text+0x6d): undefined reference to `PQsetdbLogin'
/tmp/ccIKrZnW.o(.text+0x81): undefined reference to `PQstatus'
/tmp/ccIKrZnW.o(.text+0xb3): undefined reference to `PQerrorMessage'
/tmp/ccIKrZnW.o(.text+0xeb): undefined reference to `PQexec'
/tmp/ccIKrZnW.o(.text+0x105): undefined reference to `PQresultStatus'
/tmp/ccIKrZnW.o(.text+0x135): undefined reference to `PQclear'
/tmp/ccIKrZnW.o(.text+0x153): undefined reference to `PQclear'
/tmp/ccIKrZnW.o(.text+0x167): undefined reference to `PQexec'
/tmp/ccIKrZnW.o(.text+0x181): undefined reference to `PQresultStatus'
/tmp/ccIKrZnW.o(.text+0x1b1): undefined reference to `PQclear'
/tmp/ccIKrZnW.o(.text+0x1cf): undefined reference to `PQclear'
/tmp/ccIKrZnW.o(.text+0x1e3): undefined reference to `PQexec'
/tmp/ccIKrZnW.o(.text+0x1fd): undefined reference to `PQresultStatus'
/tmp/ccIKrZnW.o(.text+0x22d): undefined reference to `PQclear'
/tmp/ccIKrZnW.o(.text+0x24b): undefined reference to `PQnfields'
/tmp/ccIKrZnW.o(.text+0x27b): undefined reference to `PQfname'
/tmp/ccIKrZnW.o(.text+0x2b8): undefined reference to `PQntuples'
/tmp/ccIKrZnW.o(.text+0x2ef): undefined reference to `PQgetvalue'
/tmp/ccIKrZnW.o(.text+0x32c): undefined reference to `PQclear'
/tmp/ccIKrZnW.o(.text+0x340): undefined reference to `PQexec'
/tmp/ccIKrZnW.o(.text+0x354): undefined reference to `PQclear'
/tmp/ccIKrZnW.o(.text+0x368): undefined reference to `PQexec'
/tmp/ccIKrZnW.o(.text+0x37c): undefined reference to `PQclear'
/tmp/ccIKrZnW.o(.text+0x38b): undefined reference to `PQfinish'


Please can you help me with this two problems??? Thank you

The C program is this one:

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

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

main()
{
    char       *pghost,
               *pgport,
               *pgoptions,
               *pgtty;
    char       *dbName;
    int         nFields;
    int         i,
                j;

    /* FILE *debug; */

    PGconn     *conn;
    PGresult   *res;

    /*
     * begin, by setting the parameters for a backend connection if the
     * parameters are null, then the system will try to use reasonable
     * defaults by looking up environment variables or, failing that,
     * using hardwired constants
     */
    pghost = NULL;              /* host name of the backend server */
    pgport = NULL;              /* port of the backend server */
    pgoptions = NULL;           /* special options to start up the backend
                                 * server */
    pgtty = NULL;               /* debugging tty for the backend server */
    dbName = "template1";

    /* make a connection to the database */
    conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);

    /*
     * check to see that the backend connection was successfully made
     */
    if (PQstatus(conn) == CONNECTION_BAD)
    {
        fprintf(stderr, "Connection to database '%s' failed.\n", dbName);
        fprintf(stderr, "%s", PQerrorMessage(conn));
        exit_nicely(conn);
    }

    /* debug = fopen("/tmp/trace.out","w"); */
    /* PQtrace(conn, debug);  */

    /* start a transaction block */
    res = PQexec(conn, "BEGIN");
    if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
    {
        fprintf(stderr, "BEGIN command failed\n");
        PQclear(res);
        exit_nicely(conn);
    }

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

    /*
     * fetch instances from the pg_database, the system catalog of
     * databases
     */
    res = PQexec(conn, "DECLARE mycursor CURSOR FOR select * from
pg_database");
    if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
    {
        fprintf(stderr, "DECLARE CURSOR command failed\n");
        PQclear(res);
        exit_nicely(conn);
    }
    PQclear(res);
    res = PQexec(conn, "FETCH ALL in mycursor");
    if (!res || PQresultStatus(res) != PGRES_TUPLES_OK)
    {
        fprintf(stderr, "FETCH ALL command didn't return tuples
properly\n");
        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 instances */
    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 cursor */
    res = PQexec(conn, "CLOSE mycursor");
    PQclear(res);

    /* commit the transaction */
    res = PQexec(conn, "COMMIT");
    PQclear(res);

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

    /* fclose(debug); */
    return 0;

}

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