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libpq

PostgreSQL's official application interface library for the C programming language

libpq is the official C application programming interface to PostgreSQL, providing a set of library functions enabling client applications to communicate with a PostgreSQL server.

Other application interfaces such as C++, Perl, Python, Tcl and ECPG, as well as client applications such as psql, are based on libpq and inherit some of its behaviour and environment configuration.

Historical note: the "pq" in libpq derives from PostQUEL (see A Brief History of PostgreSQL).

Change history

Incomplete, work in progress!

Examples

The following example code demonstrates how to use libpq to connect to a PostgreSQL server and execute a simple query - "SELECT 'hello world'" - and display the output.

#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;

    if (argc > 1)
        conninfo = argv[1];
    else
        conninfo = "dbname=postgres";

    /* Connect to the database */
    conn = PQconnectdb(conninfo);

    /* Verify success of database connection */
    if (PQstatus(conn) != CONNECTION_OK)
    {
        fprintf(stderr, "Connection to database failed: %s",
                PQerrorMessage(conn));
        exit_nicely(conn);
    }

    /* Execute a simple query and display the results */
    res = PQexec(conn, "SELECT 'Hello World'");
    printf("%s\n", PQgetvalue(res, 0, 0));

    PQclear(res);

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

    return 0;
}

Further examples can be found in the PostgreSQL manual and in the directory src/test/examples/ in the PostgreSQL source code distribution.

Categories

Application interface