Thread

1. A PGLIB lo_export function for Win32

   Scott Holmes <sholmes@pacificnet.net> — 2001-07-05T21:20:18Z

   Well, I'm making progress in my attempt to incorporate large objects in my NT 
   application.  At this point I can export an object but the resulting file is 
   corrupt.  The object within the database is not corrupt.  I have checked by 
   using the normal lo_export function.  Following is the section of code used to 
   create the file.  I have removed the error checks for readability here.  The 
   normal C function calls open(), write(), and close() as well as the single 
   call to lo_export() produce  the corrupted file,  the commented out Win32 
   calls cause a memory fault.
   
   
     res = PQexec(conn, "begin");
     PQclear(res);
   
     lobj_fd = lo_open(conn, lobjId, INV_READ); 
   
   /*  lo_export(conn, lobjId, filename);  */
   
     fd = open(filename, OF_CREATE | OF_WRITE, 0666); 
   
   /*  fd = CreateFile(filename, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_DELETE 
   | FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, CREATE_ALWAYS, 
   FILE_ATTRIBUTE_NORMAL, NULL); */
   
     while ((nbytes = lo_read(conn, lobj_fd, buf, BUFSIZE)) > 0)
     {
       tmp = write(fd, buf, nbytes); 
   
   /*    tmp =WriteFile(fd, buf, nbytes, BUFSIZE, NULL); */
   
     }
   
   /*  (void) lo_close(conn, lobj_fd); */
   
     (void) close(fd); 
     (void) CloseHandle(fd);
   
     res = PQexec(conn, "end");
     PQclear(res);
     PQfinish(conn);
   
   
   

2. Re: A PGLIB lo_export function for Win32

   Eric G. Miller <egm2@jps.net> — 2001-07-06T02:20:29Z

   On Thu, Jul 05, 2001 at 02:20:18PM -0700, Scott Holmes wrote:
   > Well, I'm making progress in my attempt to incorporate large objects in my NT 
   > application.  At this point I can export an object but the resulting file is 
   > corrupt.  The object within the database is not corrupt.  I have checked by 
   > using the normal lo_export function.  Following is the section of code used to 
   > create the file.  I have removed the error checks for readability here.  The 
   > normal C function calls open(), write(), and close() as well as the single 
   > call to lo_export() produce  the corrupted file,  the commented out Win32 
   > calls cause a memory fault.
   
   open(), write() and close() are not standard C.  Maybe you'd prefer to
   use fopen(), fwrite() and fclose()?
   
   >   res = PQexec(conn, "begin");
   >   PQclear(res);
   > 
   >   lobj_fd = lo_open(conn, lobjId, INV_READ); 
   > 
   > /*  lo_export(conn, lobjId, filename);  */
   > 
   >   fd = open(filename, OF_CREATE | OF_WRITE, 0666); 
                           ^^^^^^^^^^^^^^^^^^^^
   			What are these symbols?  Are they windows'isms?
   			O_CREAT | O_TRUNC | O_WRONLY
   
     But maybe, 'fopen (filename, "wb");'  would be more portable?  Make
     sure to use "wb" on Windows which does sh*t behind your back if you
     don't and you really want a binary file.
   
   > /*  fd = CreateFile(filename, GENERIC_READ | GENERIC_WRITE, FILE_SHARE_DELETE 
   > | FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, CREATE_ALWAYS, 
   > FILE_ATTRIBUTE_NORMAL, NULL); */
   > 
   >   while ((nbytes = lo_read(conn, lobj_fd, buf, BUFSIZE)) > 0)
   >   {
   >     tmp = write(fd, buf, nbytes); 
   
         Generally, this shouldn't fail for regular files, but why capture
         the bytes written if you aren't going to do something with it?
         
   > 
   > /*    tmp =WriteFile(fd, buf, nbytes, BUFSIZE, NULL); */
   > 
   >   }
   > 
   > /*  (void) lo_close(conn, lobj_fd); */
   > 
   >   (void) close(fd); 
   >   (void) CloseHandle(fd);
       
       What are these (void) casts for? And what's the difference between
       close(fd) and CloseHandle(fd) ?  Looks like you're closing the same
       file twice.  That should generate an error.
   
   >   res = PQexec(conn, "end");
   >   PQclear(res);
   >   PQfinish(conn);
   
   -- 
   Eric G. Miller <egm2@jps.net>