SQLite

#define restoreCursorPosition(p) \
  (p->eState>=CURSOR_REQUIRESEEK ? \
         btreeRestoreCursorPosition(p) : \
         SQLITE_OK)

/*
** Determine whether or not a cursor has moved from the position it
** was last placed at.  Cursors can move when the row they are pointing
** at is deleted out from under them.
** Determine whether or not a cursor has moved from the position where
** it was last placed, or has been invalidated for any other reason.
** Cursors can move when the row they are pointing at is deleted out
** from under them, for example.  Cursor might also move if a btree
** is rebalanced.
**
** This routine returns an error code if something goes wrong.  The
** Calling this routine with a NULL cursor pointer returns false.
** integer *pHasMoved is set as follows:
**
**    0:   The cursor is unchanged
** Use the separate sqlite3BtreeCursorRestore() routine to restore a cursor
**    1:   The cursor is still pointing at the same row, but the pointers
**         returned by sqlite3BtreeKeyFetch() or sqlite3BtreeDataFetch()
**         might now be invalid because of a balance() or other change to the
** back to where it ought to be if this routine returns true.
*/
int sqlite3BtreeCursorHasMoved(BtCursor *pCur){
  return pCur && pCur->eState!=CURSOR_VALID;
}

**         b-tree.
**    2:   The cursor is no longer pointing to the row.  The row might have
**         been deleted out from under the cursor.
/*
** This routine restores a cursor back to its original position after it
** has been moved by some outside activity (such as a btree rebalance or
** a row having been deleted out from under the cursor).  
**
** On success, the *pDifferentRow parameter is false if the cursor is left
** pointing at exactly the same row.  *pDifferntRow is the row the cursor
** was pointing to has been deleted, forcing the cursor to point to some
** nearby row.
**
** This routine should only be called for a cursor that just returned
** TRUE from sqlite3BtreeCursorHasMoved().
*/
int sqlite3BtreeCursorHasMoved(BtCursor *pCur, int *pHasMoved){
int sqlite3BtreeCursorRestore(BtCursor *pCur, int *pDifferentRow){
  int rc;

  assert( pCur!=0 );
  if( pCur->eState==CURSOR_VALID ){
  assert( pCur->eState!=CURSOR_VALID );
    *pHasMoved = 0;
    return SQLITE_OK;
  }
  rc = restoreCursorPosition(pCur);
  if( rc ){
    *pHasMoved = 2;
    *pDifferentRow = 1;
    return rc;
  }
  if( pCur->eState!=CURSOR_VALID || NEVER(pCur->skipNext!=0) ){
    *pHasMoved = 2;
    *pDifferentRow = 1;
  }else{
    *pHasMoved = 1;
    *pDifferentRow = 0;
  }
  return SQLITE_OK;
}

#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** Given a page number of a regular database page, return the page

int sqlite3BtreeMovetoUnpacked(
  BtCursor*,
  UnpackedRecord *pUnKey,
  i64 intKey,
  int bias,
  int *pRes
);
int sqlite3BtreeCursorHasMoved(BtCursor*, int*);
int sqlite3BtreeCursorHasMoved(BtCursor*);
int sqlite3BtreeCursorRestore(BtCursor*, int*);
int sqlite3BtreeDelete(BtCursor*);
int sqlite3BtreeInsert(BtCursor*, const void *pKey, i64 nKey,
                                  const void *pData, int nData,
                                  int nZero, int bias, int seekResult);
int sqlite3BtreeFirst(BtCursor*, int *pRes);
int sqlite3BtreeLast(BtCursor*, int *pRes);
int sqlite3BtreeNext(BtCursor*, int *pRes);

  if( p->pNext ){
    p->pNext->pPrev = p->pPrev;
  }
  p->magic = VDBE_MAGIC_DEAD;
  p->db = 0;
  sqlite3DbFree(db, p);
}

/*
** The cursor "p" has a pending seek operation that has not yet been
** carried out.  Seek the cursor now.  If an error occurs, return
** the appropriate error code.
*/
static int SQLITE_NOINLINE handleDeferredMoveto(VdbeCursor *p){
  int res, rc;
#ifdef SQLITE_TEST
  extern int sqlite3_search_count;
#endif
  assert( p->deferredMoveto );
  assert( p->isTable );
  rc = sqlite3BtreeMovetoUnpacked(p->pCursor, 0, p->movetoTarget, 0, &res);
  if( rc ) return rc;
  p->lastRowid = p->movetoTarget;
  if( res!=0 ) return SQLITE_CORRUPT_BKPT;
  p->rowidIsValid = 1;
#ifdef SQLITE_TEST
  sqlite3_search_count++;
#endif
  p->deferredMoveto = 0;
  p->cacheStatus = CACHE_STALE;
  return SQLITE_OK;
}

/*
** Something has moved cursor "p" out of place.  Maybe the row it was
** pointed to was deleted out from under it.  Or maybe the btree was
** rebalanced.  Whatever the cause, try to restore "p" to the place it
** is suppose to be pointing.  If the row was deleted out from under the
** cursor, set the cursor to point to a NULL row.
*/
static int SQLITE_NOINLINE handleMovedCursor(VdbeCursor *p){
  int isDifferentRow, rc;
  assert( p->pCursor!=0 );
  assert( sqlite3BtreeCursorHasMoved(p->pCursor) );
  rc = sqlite3BtreeCursorRestore(p->pCursor, &isDifferentRow);
  p->cacheStatus = CACHE_STALE;
  if( isDifferentRow ) p->nullRow = 1;
  return rc;
}

/*
** Make sure the cursor p is ready to read or write the row to which it
** was last positioned.  Return an error code if an OOM fault or I/O error
** prevents us from positioning the cursor to its correct position.
**
** If a MoveTo operation is pending on the given cursor, then do that
** MoveTo now.  If no move is pending, check to see if the row has been
** deleted out from under the cursor and if it has, mark the row as
** a NULL row.
**
** If the cursor is already pointing to the correct row and that row has
** not been deleted out from under the cursor, then this routine is a no-op.
*/
int sqlite3VdbeCursorMoveto(VdbeCursor *p){
  if( p->deferredMoveto ){
    int res, rc;
#ifdef SQLITE_TEST
    extern int sqlite3_search_count;
#endif
    assert( p->isTable );
    rc = sqlite3BtreeMovetoUnpacked(p->pCursor, 0, p->movetoTarget, 0, &res);
    if( rc ) return rc;
    p->lastRowid = p->movetoTarget;
    if( res!=0 ) return SQLITE_CORRUPT_BKPT;
    p->rowidIsValid = 1;
#ifdef SQLITE_TEST
    sqlite3_search_count++;
#endif
    p->deferredMoveto = 0;
    return handleDeferredMoveto(p);
    p->cacheStatus = CACHE_STALE;
  }else if( p->pCursor ){
    int hasMoved;
    int rc = sqlite3BtreeCursorHasMoved(p->pCursor, &hasMoved);
    if( rc ) return rc;
    if( hasMoved ){
      p->cacheStatus = CACHE_STALE;
      if( hasMoved==2 ) p->nullRow = 1;
    }
  }
  if( sqlite3BtreeCursorHasMoved(p->pCursor) ){
    return handleMovedCursor(p);
  }
  return SQLITE_OK;
}

/*
** The following functions:
**