| PostgreSQL 9.1.14 Documentation | ||||
|---|---|---|---|---|
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   Large objects are not directly supported by ECPG, but ECPG
   application can manipulate large objects through the libpq large
   object functions, obtaining the necessary PGconn
   object by calling the ECPGget_PGconn()
   function.  (However, use of
   the ECPGget_PGconn() function and touching
   PGconn objects directly should be done very carefully
   and ideally not mixed with other ECPG database access calls.)
  
   For more details about the ECPGget_PGconn(), see
   Section 33.11.  For information about the large
   object function interface, see Chapter 32.
  
Large object functions have to be called in a transaction block, so when autocommit is off, BEGIN commands have to be issued explicitly.
Example 33-2 shows an example program that illustrates how to create, write, and read a large object in an ECPG application.
Example 33-2. ECPG Program Accessing Large Objects
#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 < 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 < 0)
        printf("lo_open() failed: %s", PQerrorMessage(conn));
    printf("fd = %d\n", fd);
    rc = lo_write(conn, fd, buf, buflen);
    if (rc < 0)
        printf("lo_write() failed\n");
    rc = lo_close(conn, fd);
    if (rc < 0)
        printf("lo_close() failed: %s", PQerrorMessage(conn));
    /* read test */
    fd = lo_open(conn, loid, INV_READ);
    if (fd < 0)
        printf("lo_open() failed: %s", PQerrorMessage(conn));
    printf("fd = %d\n", fd);
    rc = lo_read(conn, fd, buf2, buflen);
    if (rc < 0)
        printf("lo_read() failed\n");
    rc = lo_close(conn, fd);
    if (rc < 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 < 0)
        printf("lo_unlink() failed: %s", PQerrorMessage(conn));
    EXEC SQL COMMIT;
    EXEC SQL DISCONNECT ALL;
    return 0;
}