Re: A PGLIB lo_export function for Win32

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>