telldir usage
Fred Fish
fnf at estinc.UUCP
Fri Mar 31 13:49:44 AEST 1989
Is it legal to do a telldir on an open directory, close the directory,
and then come back later to open the directory and use the telldir
value in a seekdir call to pick up where you left off? I've seen
this topic discussed previously on the net, and had thought that the
consensus was that this was a special case supported by the directory
reading routines. The manual for telldir states:
seekdir sets the position of the next readdir operation on
the directory stream. The new position reverts to the one
associated with the directory stream when the telldir
operation was performed. Values returned by telldir are
good only for the lifetime of the DIR pointer from which
they are derived. If the directory is closed and then
reopened, the telldir value may be invalidated due to
undetected directory compaction.
which seems to state that such operation is not legal. However, it
then goes on to say:
It is safe to use a previous telldir value immediately after
a call to opendir and before any calls to readdir.
The sample program below works on Ultrix, the only BSD based system
I have immediate access to, but fails on a pyramid in the att universe.
The failure mode on the pyramid is that dirpos remains stuck at zero
and the program loops printing "0 ."
Similar code works fine on all of the System V machines I have access
to that have been retrofitted with the directory reading routines.
Is the pyramid broken? Does this work on most machines simply by
luck and thus breaks on the pyramid since it is "officially illegal"?
What sayeth the wizards...
================================= cut here =========================
#include <stdio.h>
#include <sys/types.h>
#ifdef SYSV
# include <sys/ndir.h>
# define DSTRUCT direct
#else
# include <dirent.h>
# define DSTRUCT dirent
#endif
main ()
{
register int needseek = 0;
register DIR *dirp = NULL;
register long dirpos = 0L;
register struct DSTRUCT *dbuf;
for (;;) {
if ((dirp = opendir (".")) == NULL) {
perror ("can't open '.'");
break;
}
if (needseek) {
seekdir (dirp, dirpos);
}
if ((dbuf = readdir (dirp)) == NULL) {
break;
} else {
dirpos = telldir (dirp);
printf ("%8ld %s\n", dirpos, dbuf -> d_name);
closedir (dirp);
needseek = 1;
}
}
if (dirp != NULL) {
closedir (dirp);
}
}
================================= cut here =========================
-Fred
--
# Fred Fish, 1835 E. Belmont Drive, Tempe, AZ 85284, USA
# 1-602-491-0048 asuvax!{nud,mcdphx}!estinc!fnf
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