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>Chapter 33. <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"
>33.12. 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 33.11</A
>. For information about the large
object function interface, see <A
HREF="largeobjects.html"
>Chapter 32</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 33-2</A
> shows an example program that
illustrates how to create, write, and read a large object in an
ECPG application.
</P
><DIV
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><P
><B
>Example 33-2. ECPG Program Accessing Large Objects</B
></P
><PRE
CLASS="PROGRAMLISTING"
>#include <stdio.h>
#include <stdlib.h>
#include <libpq-fe.h>
#include <libpq/libpq-fs.h>
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;
conn = ECPGget_PGconn("con1");
printf("conn = %p\n", conn);
/* create */
loid = lo_create(conn, 0);
if (loid &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 &lt; 0)
printf("lo_open() failed: %s", PQerrorMessage(conn));
printf("fd = %d\n", fd);
rc = lo_write(conn, fd, buf, buflen);
if (rc &lt; 0)
printf("lo_write() failed\n");
rc = lo_close(conn, fd);
if (rc &lt; 0)
printf("lo_close() failed: %s", PQerrorMessage(conn));
/* read test */
fd = lo_open(conn, loid, INV_READ);
if (fd &lt; 0)
printf("lo_open() failed: %s", PQerrorMessage(conn));
printf("fd = %d\n", fd);
rc = lo_read(conn, fd, buf2, buflen);
if (rc &lt; 0)
printf("lo_read() failed\n");
rc = lo_close(conn, fd);
if (rc &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 &lt; 0)
printf("lo_unlink() failed: %s", PQerrorMessage(conn));
EXEC SQL COMMIT;
EXEC SQL DISCONNECT ALL;
return 0;
}</PRE
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