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1<?xml version="1.0" encoding="UTF-8" standalone="no"?>2<!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>35.5. Example Program</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 Vsnapshot" /><link rel="prev" href="lo-funcs.html" title="35.4. Server-Side Functions" /><link rel="next" href="ecpg.html" title="Chapter 36. ECPG — Embedded SQL in C" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">35.5. Example Program</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="lo-funcs.html" title="35.4. Server-Side Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="largeobjects.html" title="Chapter 35. Large Objects">Up</a></td><th width="60%" align="center">Chapter 35. Large Objects</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="ecpg.html" title="Chapter 36. ECPG — Embedded SQL in C">Next</a></td></tr></table><hr /></div><div class="sect1" id="LO-EXAMPLESECT"><div class="titlepage"><div><div><h2 class="title" style="clear: both">35.5. Example Program <a href="#LO-EXAMPLESECT" class="id_link">#</a></h2></div></div></div><p>3 <a class="xref" href="lo-examplesect.html#LO-EXAMPLE" title="Example 35.1. Large Objects with libpq Example Program">Example 35.1</a> is a sample program which shows how the large object4 interface5 in <span class="application">libpq</span> can be used. Parts of the program are6 commented out but are left in the source for the reader's7 benefit. This program can also be found in8 <code class="filename">src/test/examples/testlo.c</code> in the source distribution.9</p><div class="example" id="LO-EXAMPLE"><p class="title"><strong>Example 35.1. Large Objects with <span class="application">libpq</span> Example Program</strong></p><div class="example-contents"><pre class="programlisting">10/*-----------------------------------------------------------------11 *12 * testlo.c13 * test using large objects with libpq14 *15 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group16 * Portions Copyright (c) 1994, Regents of the University of California17 *18 *19 * IDENTIFICATION20 * src/test/examples/testlo.c21 *22 *-----------------------------------------------------------------23 */24#include <stdio.h>25#include <stdlib.h>26 27#include <sys/types.h>28#include <sys/stat.h>29#include <fcntl.h>30#include <unistd.h>31 32#include "libpq-fe.h"33#include "libpq/libpq-fs.h"34 35#define BUFSIZE 102436 37/*38 * importFile -39 * import file "in_filename" into database as large object "lobjOid"40 *41 */42static Oid43importFile(PGconn *conn, char *filename)44{45 Oid lobjId;46 int lobj_fd;47 char buf[BUFSIZE];48 int nbytes,49 tmp;50 int fd;51 52 /*53 * open the file to be read in54 */55 fd = open(filename, O_RDONLY, 0666);56 if (fd < 0)57 { /* error */58 fprintf(stderr, "cannot open unix file\"%s\"\n", filename);59 }60 61 /*62 * create the large object63 */64 lobjId = lo_creat(conn, INV_READ | INV_WRITE);65 if (lobjId == 0)66 fprintf(stderr, "cannot create large object");67 68 lobj_fd = lo_open(conn, lobjId, INV_WRITE);69 70 /*71 * read in from the Unix file and write to the inversion file72 */73 while ((nbytes = read(fd, buf, BUFSIZE)) > 0)74 {75 tmp = lo_write(conn, lobj_fd, buf, nbytes);76 if (tmp < nbytes)77 fprintf(stderr, "error while reading \"%s\"", filename);78 }79 80 close(fd);81 lo_close(conn, lobj_fd);82 83 return lobjId;84}85 86static void87pickout(PGconn *conn, Oid lobjId, int start, int len)88{89 int lobj_fd;90 char *buf;91 int nbytes;92 int nread;93 94 lobj_fd = lo_open(conn, lobjId, INV_READ);95 if (lobj_fd < 0)96 fprintf(stderr, "cannot open large object %u", lobjId);97 98 lo_lseek(conn, lobj_fd, start, SEEK_SET);99 buf = malloc(len + 1);100 101 nread = 0;102 while (len - nread > 0)103 {104 nbytes = lo_read(conn, lobj_fd, buf, len - nread);105 buf[nbytes] = '\0';106 fprintf(stderr, ">>> %s", buf);107 nread += nbytes;108 if (nbytes <= 0)109 break; /* no more data? */110 }111 free(buf);112 fprintf(stderr, "\n");113 lo_close(conn, lobj_fd);114}115 116static void117overwrite(PGconn *conn, Oid lobjId, int start, int len)118{119 int lobj_fd;120 char *buf;121 int nbytes;122 int nwritten;123 int i;124 125 lobj_fd = lo_open(conn, lobjId, INV_WRITE);126 if (lobj_fd < 0)127 fprintf(stderr, "cannot open large object %u", lobjId);128 129 lo_lseek(conn, lobj_fd, start, SEEK_SET);130 buf = malloc(len + 1);131 132 for (i = 0; i < len; i++)133 buf[i] = 'X';134 buf[i] = '\0';135 136 nwritten = 0;137 while (len - nwritten > 0)138 {139 nbytes = lo_write(conn, lobj_fd, buf + nwritten, len - nwritten);140 nwritten += nbytes;141 if (nbytes <= 0)142 {143 fprintf(stderr, "\nWRITE FAILED!\n");144 break;145 }146 }147 free(buf);148 fprintf(stderr, "\n");149 lo_close(conn, lobj_fd);150}151 152 153/*154 * exportFile -155 * export large object "lobjOid" to file "out_filename"156 *157 */158static void159exportFile(PGconn *conn, Oid lobjId, char *filename)160{161 int lobj_fd;162 char buf[BUFSIZE];163 int nbytes,164 tmp;165 int fd;166 167 /*168 * open the large object169 */170 lobj_fd = lo_open(conn, lobjId, INV_READ);171 if (lobj_fd < 0)172 fprintf(stderr, "cannot open large object %u", lobjId);173 174 /*175 * open the file to be written to176 */177 fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC, 0666);178 if (fd < 0)179 { /* error */180 fprintf(stderr, "cannot open unix file\"%s\"",181 filename);182 }183 184 /*185 * read in from the inversion file and write to the Unix file186 */187 while ((nbytes = lo_read(conn, lobj_fd, buf, BUFSIZE)) > 0)188 {189 tmp = write(fd, buf, nbytes);190 if (tmp < nbytes)191 {192 fprintf(stderr, "error while writing \"%s\"",193 filename);194 }195 }196 197 lo_close(conn, lobj_fd);198 close(fd);199}200 201static void202exit_nicely(PGconn *conn)203{204 PQfinish(conn);205 exit(1);206}207 208int209main(int argc, char **argv)210{211 char *in_filename,212 *out_filename;213 char *database;214 Oid lobjOid;215 PGconn *conn;216 PGresult *res;217 218 if (argc != 4)219 {220 fprintf(stderr, "Usage: %s database_name in_filename out_filename\n",221 argv[0]);222 exit(1);223 }224 225 database = argv[1];226 in_filename = argv[2];227 out_filename = argv[3];228 229 /*230 * set up the connection231 */232 conn = PQsetdb(NULL, NULL, NULL, NULL, database);233 234 /* check to see that the backend connection was successfully made */235 if (PQstatus(conn) != CONNECTION_OK)236 {237 fprintf(stderr, "%s", PQerrorMessage(conn));238 exit_nicely(conn);239 }240 241 /* Set always-secure search path, so malicious users can't take control. */242 res = PQexec(conn,243 "SELECT pg_catalog.set_config('search_path', '', false)");244 if (PQresultStatus(res) != PGRES_TUPLES_OK)245 {246 fprintf(stderr, "SET failed: %s", PQerrorMessage(conn));247 PQclear(res);248 exit_nicely(conn);249 }250 PQclear(res);251 252 res = PQexec(conn, "begin");253 PQclear(res);254 printf("importing file \"%s\" ...\n", in_filename);255/* lobjOid = importFile(conn, in_filename); */256 lobjOid = lo_import(conn, in_filename);257 if (lobjOid == 0)258 fprintf(stderr, "%s\n", PQerrorMessage(conn));259 else260 {261 printf("\tas large object %u.\n", lobjOid);262 263 printf("picking out bytes 1000-2000 of the large object\n");264 pickout(conn, lobjOid, 1000, 1000);265 266 printf("overwriting bytes 1000-2000 of the large object with X's\n");267 overwrite(conn, lobjOid, 1000, 1000);268 269 printf("exporting large object to file \"%s\" ...\n", out_filename);270/* exportFile(conn, lobjOid, out_filename); */271 if (lo_export(conn, lobjOid, out_filename) < 0)272 fprintf(stderr, "%s\n", PQerrorMessage(conn));273 }274 275 res = PQexec(conn, "end");276 PQclear(res);277 PQfinish(conn);278 return 0;279}280 281</pre></div></div><br class="example-break" /></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="lo-funcs.html" title="35.4. 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