Sample Program

/*--------------------------------------------------------------
          *
          * testlo.c--
          *    test using large objects with libpq
          *
          * Copyright (c) 1994, Regents of the University of California
          *
          *
          * IDENTIFICATION
          *    /usr/local/devel/pglite/cvs/src/doc/manual.me,v 1.16 1995/09/01 23:55:00 jolly Exp
          *
          *--------------------------------------------------------------
          */
         #include <stdio.h>
         #include "libpq-fe.h"
         #include "libpq/libpq-fs.h"

         #define BUFSIZE          1024

         /*
          * importFile *    import file "in_filename" into database as large object "lobjOid"
          *
          */
         Oid importFile(PGconn *conn, char *filename)
         {
             Oid lobjId;
             int lobj_fd;
             char buf[BUFSIZE];
             int nbytes, tmp;
             int fd;

             /*
              * open the file to be read in
              */
             fd = open(filename, O_RDONLY, 0666);
             if (fd < 0)  {   /* error */
              fprintf(stderr, "can't open unix file %s\n", filename);
             }

             /*
              * create the large object
              */
             lobjId = lo_creat(conn, INV_READ|INV_WRITE);
             if (lobjId == 0) {
              fprintf(stderr, "can't create large object\n");
             }

             lobj_fd = lo_open(conn, lobjId, INV_WRITE);
             /*
              * read in from the Unix file and write to the inversion file
              */
             while ((nbytes = read(fd, buf, BUFSIZE)) > 0) {
              tmp = lo_write(conn, lobj_fd, buf, nbytes);
              if (tmp < nbytes) {
                  fprintf(stderr, "error while reading large object\n");
              }
             }

             (void) close(fd);
             (void) lo_close(conn, lobj_fd);

             return lobjId;
         }

         void pickout(PGconn *conn, Oid lobjId, int start, int len)
         {
             int lobj_fd;
             char* buf;
             int nbytes;
             int nread;

             lobj_fd = lo_open(conn, lobjId, INV_READ);
             if (lobj_fd < 0) {
              fprintf(stderr,"can't open large object %d\n",
                   lobjId);
             }

             lo_lseek(conn, lobj_fd, start, SEEK_SET);
             buf = malloc(len+1);

             nread = 0;
             while (len - nread > 0) {
              nbytes = lo_read(conn, lobj_fd, buf, len - nread);
              buf[nbytes] = ' ';
              fprintf(stderr,">>> %s", buf);
              nread += nbytes;
             }
             fprintf(stderr,"\n");
             lo_close(conn, lobj_fd);
         }

         void overwrite(PGconn *conn, Oid lobjId, int start, int len)
         {
             int lobj_fd;
             char* buf;
             int nbytes;
             int nwritten;
             int i;

             lobj_fd = lo_open(conn, lobjId, INV_READ);
             if (lobj_fd < 0) {
              fprintf(stderr,"can't open large object %d\n",
                   lobjId);
             }

             lo_lseek(conn, lobj_fd, start, SEEK_SET);
             buf = malloc(len+1);

             for (i=0;i<len;i++)
              buf[i] = 'X';
             buf[i] = ' ';

             nwritten = 0;
             while (len - nwritten > 0) {
              nbytes = lo_write(conn, lobj_fd, buf + nwritten, len - nwritten);
              nwritten += nbytes;
             }
             fprintf(stderr,"\n");
             lo_close(conn, lobj_fd);
         }

         /*
          * exportFile *    export large object "lobjOid" to file "out_filename"
          *
          */
         void exportFile(PGconn *conn, Oid lobjId, char *filename)
         {
             int lobj_fd;
             char buf[BUFSIZE];
             int nbytes, tmp;
             int fd;

             /*
              * create an inversion "object"
              */
             lobj_fd = lo_open(conn, lobjId, INV_READ);
             if (lobj_fd < 0) {
              fprintf(stderr,"can't open large object %d\n",
                   lobjId);
             }

             /*
              * open the file to be written to
              */
             fd = open(filename, O_CREAT|O_WRONLY, 0666);
             if (fd < 0)  {   /* error */
              fprintf(stderr, "can't open unix file %s\n",
                   filename);
             }

             /*
              * read in from the Unix file and write to the inversion file
              */
             while ((nbytes = lo_read(conn, lobj_fd, buf, BUFSIZE)) > 0) {
              tmp = write(fd, buf, nbytes);
                 if (tmp < nbytes) {
                  fprintf(stderr,"error while writing %s\n",
                       filename);
              }
             }

             (void) lo_close(conn, lobj_fd);
             (void) close(fd);

             return;
         }

         void
         exit_nicely(PGconn* conn)
         {
           PQfinish(conn);
           exit(1);
         }

         int
         main(int argc, char **argv)
         {
             char *in_filename, *out_filename;
             char *database;
             Oid lobjOid;
             PGconn *conn;
             PGresult *res;

             if (argc != 4) {
              fprintf(stderr, "Usage: %s database_name in_filename out_filename\n",
                   argv[0]);
              exit(1);
             }

             database = argv[1];
             in_filename = argv[2];
             out_filename = argv[3];

             /*
              * set up the connection
              */
             conn = PQsetdb(NULL, NULL, NULL, NULL, database);

             /* check to see that the backend connection was successfully made */
             if (PQstatus(conn) == CONNECTION_BAD) {
              fprintf(stderr,"Connection to database '%s' failed.\n", database);
              fprintf(stderr,"%s",PQerrorMessage(conn));
              exit_nicely(conn);
             }

             res = PQexec(conn, "begin");
             PQclear(res);

             printf("importing file %s\n", in_filename);
         /*  lobjOid = importFile(conn, in_filename); */
             lobjOid = lo_import(conn, in_filename);
         /*
             printf("as large object %d.\n", lobjOid);

             printf("picking out bytes 1000-2000 of the large object\n");
             pickout(conn, lobjOid, 1000, 1000);

             printf("overwriting bytes 1000-2000 of the large object with X's\n");
             overwrite(conn, lobjOid, 1000, 1000);
         */

             printf("exporting large object to file %s\n", out_filename);
         /*    exportFile(conn, lobjOid, out_filename); */
             lo_export(conn, lobjOid,out_filename);

             res = PQexec(conn, "end");
             PQclear(res);
             PQfinish(conn);
             exit(0);
         }