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>Chapter 34. <SPAN
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>ECPG</SPAN
> - Embedded <ACRONYM
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>SQL</ACRONYM
> in C</TD
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><A
NAME="ECPG-LO"
>34.12. Large Objects</A
></H1
><P
>   Large objects are not directly supported by ECPG, but ECPG
   application can manipulate large objects through the libpq large
   object functions, obtaining the necessary <TT
CLASS="TYPE"
>PGconn</TT
>
   object by calling the <CODE
CLASS="FUNCTION"
>ECPGget_PGconn()</CODE
>
   function.  (However, use of
   the <CODE
CLASS="FUNCTION"
>ECPGget_PGconn()</CODE
> function and touching
   <TT
CLASS="TYPE"
>PGconn</TT
> objects directly should be done very carefully
   and ideally not mixed with other ECPG database access calls.)
  </P
><P
>   For more details about the <CODE
CLASS="FUNCTION"
>ECPGget_PGconn()</CODE
>, see
   <A
HREF="ecpg-library.html"
>Section 34.11</A
>.  For information about the large
   object function interface, see <A
HREF="largeobjects.html"
>Chapter 33</A
>.
  </P
><P
>   Large object functions have to be called in a transaction block, so
   when autocommit is off, <TT
CLASS="COMMAND"
>BEGIN</TT
> commands have to
   be issued explicitly.
  </P
><P
>   <A
HREF="ecpg-lo.html#ECPG-LO-EXAMPLE"
>Example 34-2</A
> shows an example program that
   illustrates how to create, write, and read a large object in an
   ECPG application.
  </P
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><P
><B
>Example 34-2. ECPG Program Accessing Large Objects</B
></P
><PRE
CLASS="PROGRAMLISTING"
>#include &#60;stdio.h&#62;
#include &#60;stdlib.h&#62;
#include &#60;libpq-fe.h&#62;
#include &#60;libpq/libpq-fs.h&#62;

EXEC SQL WHENEVER SQLERROR STOP;

int
main(void)
{
    PGconn     *conn;
    Oid         loid;
    int         fd;
    char        buf[256];
    int         buflen = 256;
    char        buf2[256];
    int         rc;

    memset(buf, 1, buflen);

    EXEC SQL CONNECT TO testdb AS con1;
    EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT;

    conn = ECPGget_PGconn("con1");
    printf("conn = %p\n", conn);

    /* create */
    loid = lo_create(conn, 0);
    if (loid &#38;lt; 0)
        printf("lo_create() failed: %s", PQerrorMessage(conn));

    printf("loid = %d\n", loid);

    /* write test */
    fd = lo_open(conn, loid, INV_READ|INV_WRITE);
    if (fd &#38;lt; 0)
        printf("lo_open() failed: %s", PQerrorMessage(conn));

    printf("fd = %d\n", fd);

    rc = lo_write(conn, fd, buf, buflen);
    if (rc &#38;lt; 0)
        printf("lo_write() failed\n");

    rc = lo_close(conn, fd);
    if (rc &#38;lt; 0)
        printf("lo_close() failed: %s", PQerrorMessage(conn));

    /* read test */
    fd = lo_open(conn, loid, INV_READ);
    if (fd &#38;lt; 0)
        printf("lo_open() failed: %s", PQerrorMessage(conn));

    printf("fd = %d\n", fd);

    rc = lo_read(conn, fd, buf2, buflen);
    if (rc &#38;lt; 0)
        printf("lo_read() failed\n");

    rc = lo_close(conn, fd);
    if (rc &#38;lt; 0)
        printf("lo_close() failed: %s", PQerrorMessage(conn));

    /* check */
    rc = memcmp(buf, buf2, buflen);
    printf("memcmp() = %d\n", rc);

    /* cleanup */
    rc = lo_unlink(conn, loid);
    if (rc &#38;lt; 0)
        printf("lo_unlink() failed: %s", PQerrorMessage(conn));

    EXEC SQL COMMIT;
    EXEC SQL DISCONNECT ALL;
    return 0;
}</PRE
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