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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>33.21. Example Programs</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets V1.79.1" /><link rel="prev" href="libpq-build.html" title="33.20. Building libpq Programs" /><link rel="next" href="largeobjects.html" title="Chapter 34. Large Objects" /></head><body id="docContent" class="container-fluid col-10"><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">33.21. Example Programs</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="libpq-build.html" title="33.20. Building libpq Programs">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="libpq.html" title="Chapter 33. libpq — C Library">Up</a></td><th width="60%" align="center">Chapter 33. <span xmlns="http://www.w3.org/1999/xhtml" class="application">libpq</span> — C Library</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="largeobjects.html" title="Chapter 34. Large Objects">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="LIBPQ-EXAMPLE"><div class="titlepage"><div><div><h2 class="title" style="clear: both">33.21. Example Programs</h2></div></div></div><p>
These examples and others can be found in the
directory <code class="filename">src/test/examples</code> in the source code
distribution.
</p><div class="example" id="LIBPQ-EXAMPLE-1"><p class="title"><strong>Example 33.1. <span class="application">libpq</span> Example Program 1</strong></p><div class="example-contents"><pre class="programlisting">
/*
* src/test/examples/testlibpq.c
*
*
* 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);
}
/* Set always-secure search path, so malicious users can't take control. */
res = PQexec(conn,
"SELECT pg_catalog.set_config('search_path', '', false)");
if (PQresultStatus(res) != PGRES_TUPLES_OK)
{
fprintf(stderr, "SET failed: %s", PQerrorMessage(conn));
PQclear(res);
exit_nicely(conn);
}
/*
* Should PQclear PGresult whenever it is no longer needed to avoid memory
* leaks
*/
PQclear(res);
/*
* 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);
}
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;
}
</pre></div></div><br class="example-break" /><div class="example" id="LIBPQ-EXAMPLE-2"><p class="title"><strong>Example 33.2. <span class="application">libpq</span> Example Program 2</strong></p><div class="example-contents"><pre class="programlisting">
/*
* src/test/examples/testlibpq2.c
*
*
* testlibpq2.c
* Test of the asynchronous notification interface
*
* Start this program, then from psql in another window do
* NOTIFY TBL2;
* Repeat four times to get this program to exit.
*
* Or, if you want to get fancy, try this:
* populate a database with the following commands
* (provided in src/test/examples/testlibpq2.sql):
*
* CREATE SCHEMA TESTLIBPQ2;
* SET search_path = TESTLIBPQ2;
* CREATE TABLE TBL1 (i int4);
* CREATE TABLE TBL2 (i int4);
* CREATE RULE r1 AS ON INSERT TO TBL1 DO
* (INSERT INTO TBL2 VALUES (new.i); NOTIFY TBL2);
*
* Start this program, then from psql do this four times:
*
* INSERT INTO TESTLIBPQ2.TBL1 VALUES (10);
*/
#ifdef WIN32
#include <windows.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/time.h>
#include <sys/types.h>
#ifdef HAVE_SYS_SELECT_H
#include <sys/select.h>
#endif
#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;
PGnotify *notify;
int nnotifies;
/*
* 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);
}
/* Set always-secure search path, so malicious users can't take control. */
res = PQexec(conn,
"SELECT pg_catalog.set_config('search_path', '', false)");
if (PQresultStatus(res) != PGRES_TUPLES_OK)
{
fprintf(stderr, "SET failed: %s", PQerrorMessage(conn));
PQclear(res);
exit_nicely(conn);
}
/*
* Should PQclear PGresult whenever it is no longer needed to avoid memory
* leaks
*/
PQclear(res);
/*
* Issue LISTEN command to enable notifications from the rule's NOTIFY.
*/
res = PQexec(conn, "LISTEN TBL2");
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "LISTEN command failed: %s", PQerrorMessage(conn));
PQclear(res);
exit_nicely(conn);
}
PQclear(res);
/* Quit after four notifies are received. */
nnotifies = 0;
while (nnotifies < 4)
{
/*
* Sleep until something happens on the connection. We use select(2)
* to wait for input, but you could also use poll() or similar
* facilities.
*/
int sock;
fd_set input_mask;
sock = PQsocket(conn);
if (sock < 0)
break; /* shouldn't happen */
FD_ZERO(&input_mask);
FD_SET(sock, &input_mask);
if (select(sock + 1, &input_mask, NULL, NULL, NULL) < 0)
{
fprintf(stderr, "select() failed: %s\n", strerror(errno));
exit_nicely(conn);
}
/* Now check for input */
PQconsumeInput(conn);
while ((notify = PQnotifies(conn)) != NULL)
{
fprintf(stderr,
"ASYNC NOTIFY of '%s' received from backend PID %d\n",
notify->relname, notify->be_pid);
PQfreemem(notify);
nnotifies++;
PQconsumeInput(conn);
}
}
fprintf(stderr, "Done.\n");
/* close the connection to the database and cleanup */
PQfinish(conn);
return 0;
}
</pre></div></div><br class="example-break" /><div class="example" id="LIBPQ-EXAMPLE-3"><p class="title"><strong>Example 33.3. <span class="application">libpq</span> Example Program 3</strong></p><div class="example-contents"><pre class="programlisting">
/*
* src/test/examples/testlibpq3.c
*
*
* testlibpq3.c
* Test out-of-line parameters and binary I/O.
*
* Before running this, populate a database with the following commands
* (provided in src/test/examples/testlibpq3.sql):
*
* CREATE SCHEMA testlibpq3;
* SET search_path = testlibpq3;
* SET standard_conforming_strings = ON;
* CREATE TABLE test1 (i int4, t text, b bytea);
* INSERT INTO test1 values (1, 'joe''s place', '\000\001\002\003\004');
* INSERT INTO test1 values (2, 'ho there', '\004\003\002\001\000');
*
* The expected output is:
*
* tuple 0: got
* i = (4 bytes) 1
* t = (11 bytes) 'joe's place'
* b = (5 bytes) \000\001\002\003\004
*
* tuple 0: got
* i = (4 bytes) 2
* t = (8 bytes) 'ho there'
* b = (5 bytes) \004\003\002\001\000
*/
#ifdef WIN32
#include <windows.h>
#endif
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <sys/types.h>
#include "libpq-fe.h"
/* for ntohl/htonl */
#include <netinet/in.h>
#include <arpa/inet.h>
static void
exit_nicely(PGconn *conn)
{
PQfinish(conn);
exit(1);
}
/*
* This function prints a query result that is a binary-format fetch from
* a table defined as in the comment above. We split it out because the
* main() function uses it twice.
*/
static void
show_binary_results(PGresult *res)
{
int i,
j;
int i_fnum,
t_fnum,
b_fnum;
/* Use PQfnumber to avoid assumptions about field order in result */
i_fnum = PQfnumber(res, "i");
t_fnum = PQfnumber(res, "t");
b_fnum = PQfnumber(res, "b");
for (i = 0; i < PQntuples(res); i++)
{
char *iptr;
char *tptr;
char *bptr;
int blen;
int ival;
/* Get the field values (we ignore possibility they are null!) */
iptr = PQgetvalue(res, i, i_fnum);
tptr = PQgetvalue(res, i, t_fnum);
bptr = PQgetvalue(res, i, b_fnum);
/*
* The binary representation of INT4 is in network byte order, which
* we'd better coerce to the local byte order.
*/
ival = ntohl(*((uint32_t *) iptr));
/*
* The binary representation of TEXT is, well, text, and since libpq
* was nice enough to append a zero byte to it, it'll work just fine
* as a C string.
*
* The binary representation of BYTEA is a bunch of bytes, which could
* include embedded nulls so we have to pay attention to field length.
*/
blen = PQgetlength(res, i, b_fnum);
printf("tuple %d: got\n", i);
printf(" i = (%d bytes) %d\n",
PQgetlength(res, i, i_fnum), ival);
printf(" t = (%d bytes) '%s'\n",
PQgetlength(res, i, t_fnum), tptr);
printf(" b = (%d bytes) ", blen);
for (j = 0; j < blen; j++)
printf("\\%03o", bptr[j]);
printf("\n\n");
}
}
int
main(int argc, char **argv)
{
const char *conninfo;
PGconn *conn;
PGresult *res;
const char *paramValues[1];
int paramLengths[1];
int paramFormats[1];
uint32_t binaryIntVal;
/*
* 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);
}
/* Set always-secure search path, so malicious users can't take control. */
res = PQexec(conn, "SET search_path = testlibpq3");
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "SET failed: %s", PQerrorMessage(conn));
PQclear(res);
exit_nicely(conn);
}
PQclear(res);
/*
* The point of this program is to illustrate use of PQexecParams() with
* out-of-line parameters, as well as binary transmission of data.
*
* This first example transmits the parameters as text, but receives the
* results in binary format. By using out-of-line parameters we can avoid
* a lot of tedious mucking about with quoting and escaping, even though
* the data is text. Notice how we don't have to do anything special with
* the quote mark in the parameter value.
*/
/* Here is our out-of-line parameter value */
paramValues[0] = "joe's place";
res = PQexecParams(conn,
"SELECT * FROM test1 WHERE t = $1",
1, /* one param */
NULL, /* let the backend deduce param type */
paramValues,
NULL, /* don't need param lengths since text */
NULL, /* default to all text params */
1); /* ask for binary results */
if (PQresultStatus(res) != PGRES_TUPLES_OK)
{
fprintf(stderr, "SELECT failed: %s", PQerrorMessage(conn));
PQclear(res);
exit_nicely(conn);
}
show_binary_results(res);
PQclear(res);
/*
* In this second example we transmit an integer parameter in binary form,
* and again retrieve the results in binary form.
*
* Although we tell PQexecParams we are letting the backend deduce
* parameter type, we really force the decision by casting the parameter
* symbol in the query text. This is a good safety measure when sending
* binary parameters.
*/
/* Convert integer value "2" to network byte order */
binaryIntVal = htonl((uint32_t) 2);
/* Set up parameter arrays for PQexecParams */
paramValues[0] = (char *) &binaryIntVal;
paramLengths[0] = sizeof(binaryIntVal);
paramFormats[0] = 1; /* binary */
res = PQexecParams(conn,
"SELECT * FROM test1 WHERE i = $1::int4",
1, /* one param */
NULL, /* let the backend deduce param type */
paramValues,
paramLengths,
paramFormats,
1); /* ask for binary results */
if (PQresultStatus(res) != PGRES_TUPLES_OK)
{
fprintf(stderr, "SELECT failed: %s", PQerrorMessage(conn));
PQclear(res);
exit_nicely(conn);
}
show_binary_results(res);
PQclear(res);
/* close the connection to the database and cleanup */
PQfinish(conn);
return 0;
}
</pre></div></div><br class="example-break" /></div><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navfooter"><hr></hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="libpq-build.html" title="33.20. Building libpq Programs">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="libpq.html" title="Chapter 33. libpq — C Library">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="largeobjects.html" title="Chapter 34. Large Objects">Next</a></td></tr><tr><td width="40%" align="left" valign="top">33.20. Building <span xmlns="http://www.w3.org/1999/xhtml" class="application">libpq</span> Programs </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 13.4 Documentation">Home</a></td><td width="40%" align="right" valign="top"> Chapter 34. Large Objects</td></tr></table></div></body></html>
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