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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>36.12. Large Objects</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="ecpg-library.html" title="36.11. Library Functions" /><link rel="next" href="ecpg-cpp.html" title="36.13. C++ Applications" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">36.12. Large Objects</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="ecpg-library.html" title="36.11. Library Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="ecpg.html" title="Chapter 36. ECPG — Embedded SQL in C">Up</a></td><th width="60%" align="center">Chapter 36. <span class="application">ECPG</span> — Embedded <acronym class="acronym">SQL</acronym> in C</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-cpp.html" title="36.13. C++ Applications">Next</a></td></tr></table><hr /></div><div class="sect1" id="ECPG-LO"><div class="titlepage"><div><div><h2 class="title" style="clear: both">36.12. Large Objects <a href="#ECPG-LO" class="id_link">#</a></h2></div></div></div><p>3   Large objects are not directly supported by ECPG, but ECPG4   application can manipulate large objects through the libpq large5   object functions, obtaining the necessary <code class="type">PGconn</code>6   object by calling the <code class="function">ECPGget_PGconn()</code>7   function.  (However, use of8   the <code class="function">ECPGget_PGconn()</code> function and touching9   <code class="type">PGconn</code> objects directly should be done very carefully10   and ideally not mixed with other ECPG database access calls.)11  </p><p>12   For more details about the <code class="function">ECPGget_PGconn()</code>, see13   <a class="xref" href="ecpg-library.html" title="36.11. Library Functions">Section 36.11</a>.  For information about the large14   object function interface, see <a class="xref" href="largeobjects.html" title="Chapter 35. Large Objects">Chapter 35</a>.15  </p><p>16   Large object functions have to be called in a transaction block, so17   when autocommit is off, <code class="command">BEGIN</code> commands have to18   be issued explicitly.19  </p><p>20   <a class="xref" href="ecpg-lo.html#ECPG-LO-EXAMPLE" title="Example 36.2. ECPG Program Accessing Large Objects">Example 36.2</a> shows an example program that21   illustrates how to create, write, and read a large object in an22   ECPG application.23  </p><div class="example" id="ECPG-LO-EXAMPLE"><p class="title"><strong>Example 36.2. ECPG Program Accessing Large Objects</strong></p><div class="example-contents"><pre class="programlisting">24#include &lt;stdio.h&gt;25#include &lt;stdlib.h&gt;26#include &lt;libpq-fe.h&gt;27#include &lt;libpq/libpq-fs.h&gt;28 29EXEC SQL WHENEVER SQLERROR STOP;30 31int32main(void)33{34    PGconn     *conn;35    Oid         loid;36    int         fd;37    char        buf[256];38    int         buflen = 256;39    char        buf2[256];40    int         rc;41 42    memset(buf, 1, buflen);43 44    EXEC SQL CONNECT TO testdb AS con1;45    EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT;46 47    conn = ECPGget_PGconn("con1");48    printf("conn = %p\n", conn);49 50    /* create */51    loid = lo_create(conn, 0);52    if (loid &amp;lt; 0)53        printf("lo_create() failed: %s", PQerrorMessage(conn));54 55    printf("loid = %d\n", loid);56 57    /* write test */58    fd = lo_open(conn, loid, INV_READ|INV_WRITE);59    if (fd &amp;lt; 0)60        printf("lo_open() failed: %s", PQerrorMessage(conn));61 62    printf("fd = %d\n", fd);63 64    rc = lo_write(conn, fd, buf, buflen);65    if (rc &amp;lt; 0)66        printf("lo_write() failed\n");67 68    rc = lo_close(conn, fd);69    if (rc &amp;lt; 0)70        printf("lo_close() failed: %s", PQerrorMessage(conn));71 72    /* read test */73    fd = lo_open(conn, loid, INV_READ);74    if (fd &amp;lt; 0)75        printf("lo_open() failed: %s", PQerrorMessage(conn));76 77    printf("fd = %d\n", fd);78 79    rc = lo_read(conn, fd, buf2, buflen);80    if (rc &amp;lt; 0)81        printf("lo_read() failed\n");82 83    rc = lo_close(conn, fd);84    if (rc &amp;lt; 0)85        printf("lo_close() failed: %s", PQerrorMessage(conn));86 87    /* check */88    rc = memcmp(buf, buf2, buflen);89    printf("memcmp() = %d\n", rc);90 91    /* cleanup */92    rc = lo_unlink(conn, loid);93    if (rc &amp;lt; 0)94        printf("lo_unlink() failed: %s", PQerrorMessage(conn));95 96    EXEC SQL COMMIT;97    EXEC SQL DISCONNECT ALL;98    return 0;99}100</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="ecpg-library.html" title="36.11. Library Functions">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ecpg.html" title="Chapter 36. ECPG — Embedded SQL in C">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ecpg-cpp.html" title="36.13. C++ Applications">Next</a></td></tr><tr><td width="40%" align="left" valign="top">36.11. Library Functions </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 36.13. <acronym class="acronym">C++</acronym> Applications</td></tr></table></div></body></html>