Path: utzoo!attcan!uunet!mcvax!np1!nikhefh!gert
From: gert@nikhefh.hep.nl (Gert Poletiek)
Newsgroups: comp.sys.atari.st
Subject: Re: Copying a file over itself
Message-ID: <489@nikhefh.hep.nl>
Date: 19 Jul 88 22:51:22 GMT
References: <4507@pasteur.Berkeley.Edu> <565@philmds.UUCP>
Reply-To: gert@nikhefh.hep.nl (Gert Poletiek)
Organization: Nikhef-H, Amsterdam (the Netherlands).
Lines: 95

In article <565@philmds.UUCP> leo@philmds.UUCP (Leo de Wit) writes:
>In article <4507@pasteur.Berkeley.Edu> landay@cory.Berkeley.EDU (James A. Landay) writes:
>>Last night (at 3AM) I accidently copied a file over itself.
>>This seems to trash the file rather than touching the date
>>or doing nothing.  Will this be fixed in the new ROM version? (Atari?)
>
>Tried it with a 14K file (i.e. copying from the Desktop), but the
>contents remained the same. The date was changed.
>Then I tried it with a simple copy program, like this:
>
>#include <stdio.h>
>#include <fcntl.h>
>#include <osbind.h>
>
>main()
>{
>   int fdi, fdo, nread;
>   char buf[BUFSIZ];
>
>   fdi = Fopen("test.dat",O_RDONLY);
>   fdo = Fopen("test.dat",O_WRONLY|O_CREAT|O_TRUNC);
>
>   while ((nread = Fread(fdi,BUFSIZ,buf)) > 0) {
>      Fwrite(fdo,nread,buf);
>   }
>   Fclose(fdi);
>   Fclose(fdo);
>}
>
>Odd enough, even though O_TRUNC was specified the contents remained the
>same (in Unix you would get an empty file). Also the date was not changed.
>Interchanging the Fopen calls didn't make any difference.
>So the next question is perhaps: what ROM version are you using now?
>
>      Leo.
>
>B.T.W. What in the world made the GEMDOS writers decide to swap the 
>second and third parameter in the Fread and Fwrite calls, compared with
>Unix read() and write() ? Since they 'leant' quite a few things from Unix,
>wouldn't it have been easier to use the same parameter ordering?


The GemDos Fopen call has no flag O_TRUNC. Sometimes GemDos is way off the
Unix standard. (certainly in speed). In order to mimic the O_TRUNC you
should have your own open call, something like this:


open ( name, mode )
char	*name;
int		mode;
{
	int		fd;
	struct	statbuf	statbuf;


	if ( mode & O_TRUNC )  {
		if ( stat ( name, &statbuf ) == 0 )  {
			if ( statbuf.attr & (F_VOLUME|F_DIR|F_READONLY) )  {
				errno = EACCDN;
				return ( OPENERR );
			}
			if ( unlink ( name ) < 0 )
				return ( OPENERR );
			mode |= O_CREAT;
		}
	}

	fd = Fopen ( name, mode & 3 );
	if ( fd < -3 && ( mode & O_CREAT ) )		 /* try to create the file */
		fd = Fcreate ( name, 0 );

	if ( fd >= 0 && ( mode & O_APPEND ) )		/* seek to EOF */
		Fseek ( 0L, fd, 2 );

	if ( fd < -3 )  {
		errno = fd;
		return ( OPENERR );
	}
	return ( fd );
}




Also notice the nice effect of writing to a 1024 byte long file with read and
write access on byte 24 for example. The file will remain 1024 bytes long!



Gert Poletiek

NIKHEF-H, Dutch National Institute for Nuclear and High Energy Physics
          Kruislaan 409, P.O.Box 41882, 1009 DB Amsterdam, The Netherlands
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