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CBASE102.ARJ
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BTPREV.C
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1991-09-23
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/* Copyright (c) 1989 Citadel */
/* All Rights Reserved */
/* #ident "@(#)btprev.c 1.5 - 91/09/23" */
#include <ansi.h>
/* ansi headers */
#include <errno.h>
/* library headers */
#include <blkio.h>
/* local headers */
#include "btree_.h"
/*man---------------------------------------------------------------------------
NAME
btprev - previous btree key
SYNOPSIS
#include <btree.h>
int btprev(btp)
btree_t *btp;
DESCRIPTION
The btprev function retreats the cursor of btree btp to the
previous key. If cursor is currently null, it will be moved to
the last key. If the cursor is currently on the last key, it
will move to null. If the tree is empty, the cursor will remain
on null.
btprev will fail if one or more of the following is true:
[EINVAL] btp is not a valid btree pointer.
[BTELOCK] btp is not locked.
[BTENOPEN] btp is not open.
SEE ALSO
btcursor, btfirst, btlast, btnext.
DIAGNOSTICS
Upon successful completion, a value of 0 is returned. Otherwise,
a value of -1 is returned, and errno set to indicate the error.
------------------------------------------------------------------------------*/
#ifdef AC_PROTO
int btprev(btree_t *btp)
#else
int btprev(btp)
btree_t *btp;
#endif
{
int terrno = 0; /* tmp errno */
/* validate arguments */
if (!bt_valid(btp)) {
errno = EINVAL;
return -1;
}
/* check if not open */
if (!(btp->flags & BTOPEN)) {
errno = BTENOPEN;
return -1;
}
/* check locks */
if (!(btp->flags & BTLOCKS)) {
errno = BTELOCK;
return -1;
}
/* move cursor to previous key in current node */
if (btp->cbtpos.node != NIL) {
if (--btp->cbtpos.key > 0) {
return 0;
}
}
/* move cursor to null */
if (btp->cbtpos.node == btp->bthdr.first) {
btp->cbtpos.node = NIL;
btp->cbtpos.key = 0;
bt_ndinit(btp, btp->cbtnp);
return 0;
}
/* move cursor to last key in prev node */
if (btp->cbtpos.node == NIL) {
btp->cbtpos.node = btp->bthdr.last;
} else {
btp->cbtpos.node = btp->cbtnp->lsib;
}
if (bt_ndget(btp, btp->cbtpos.node, btp->cbtnp) == -1) {
BTEPRINT;
terrno = errno;
btp->cbtpos.node = NIL;
btp->cbtpos.key = 0;
bt_ndinit(btp, btp->cbtnp);
errno = terrno;
return -1;
}
btp->cbtpos.key = btp->cbtnp->n;
return 0;
}