cur_n_n.h

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// ============================================================================
// Project:     Deductive Database
// Filename:    cur_n_n.h
// Purpose:     Cursor for accessing rel_n_n with given first argument.
// Last Change: 04.08.2017
// Language:    C++
// EMail:       brass@informatik.uni-halle.de
// WWW:         http://www.informatik.uni-halle.de/~brass/
// Address:     Feldschloesschen 15, D-06120 Halle (Saale), GERMANY
// Copyright:   (c) 2015-2017 by Stefan Brass
// License:     See file "LICENSE" for copying conditions.
// Note:        There is no warranty at all - this code may contain bugs.
// ============================================================================


//=============================================================================
// Include File Frame:
//=============================================================================

#ifndef CUR_N_N_INCLUDED
#define CUR_N_N_INCLUDED

//=============================================================================
// Used Types and Macros:
//=============================================================================

#ifndef VER_INCLUDED
#include "../base/ver.h"
#endif

#ifndef STR_INCLUDED
#include "../base/str.h"
#endif

#ifndef CHECK_INCLUDED
#include "../base/check.h"
#endif

#ifndef STACK_INCLUDED
#include "../bds/stack.h"
#endif

#ifndef REL_N_N_INCLUDED
#include "../rel/rel_n_n.h"
#endif


//=============================================================================
// Private Constants:
//=============================================================================

//-----------------------------------------------------------------------------
// CUR_N_N_MAGIC: Magic number (identifies objects of this class).
//-----------------------------------------------------------------------------

static const long CUR_N_N_MAGIC = 0x434E4E0AL;  // 'RNN\n'

//=============================================================================
// Class for Cursor to Relation with two non-negative integer columns:
//=============================================================================

class cur_n_n_c {
        public:

//-----------------------------------------------------------------------------
// Constructor, Destructor:
//-----------------------------------------------------------------------------

        // Constructor:
        cur_n_n_c(rel_n_n_t rel);

        // Destructor:
        ~cur_n_n_c();

//-----------------------------------------------------------------------------
// Methods:
//-----------------------------------------------------------------------------

        // open: Open cursor over the value set for column c2, given c1.
        void open(int c1);

        // fetch: Get next tuple, returns false if there is no further tuple.
        bool fetch();

        // c2: Return value of column c2 to which the cursor points.
        int c2() {
                // Check this object:
                CHECK_VALID("cur_n_n_c::c2");

                // Check state:
                CHECK(C2 >= 0, "cur_n_n_c::c2: fetch beyond end");

                // Return current value for column c2:
                return C2;
        }


        // push: Save the cursor state on a stack.
        bool push(stack_c<int> *stack) {
                // Check this object:
                CHECK_VALID("cur_n_n_c::push");

                // Save C2 and Pos:
                if(!stack->push(C2))
                        return false;
                if(!stack->push(Pos))
                        return false;

                // Ok:
                return true;
        }

        // pop: Restore the cursor state from a stack.
        void pop(stack_c<int> *stack) {
                // Check this object:
                CHECK_VALID("cur_n_n_c::pop");

                // Restore C2 and Pos (in opposite order):
                Pos = stack->pop();
                C2  = stack->pop();
        }

//-----------------------------------------------------------------------------
// Debugging Support:
//-----------------------------------------------------------------------------

#if     VER_DEBUG
        public:
        // Integrity check:
        str_t   check() const;

        private:
        // Magic number (identifies objects of this class for debugging).
        long    Magic;          // Must be "CUR_N_N_MAGIC".
#endif

#if     VER_DUMP
        public:
        // Display data structure:
        void dump(str_t headline = STR_NULL) const;
#endif

//-----------------------------------------------------------------------------
// Copy-constructor and assignment operator are not supported for this class:
//-----------------------------------------------------------------------------

        private:

        cur_n_n_c(const cur_n_n_c& obj);                // Not implemented
        cur_n_n_c& operator=(const cur_n_n_c& obj);     // Not implemented

//-----------------------------------------------------------------------------
// Private Object Members:
//-----------------------------------------------------------------------------

        private:

        // Relation, over which this cursor runs:
        rel_n_n_t Rel;

        // Current value of column c2:
        int C2;

        // Position in relation index / value list for next value:
        int Pos;

//=============================================================================
// End of Class:
//=============================================================================

};

//-----------------------------------------------------------------------------
// Define pointer type:
//-----------------------------------------------------------------------------

typedef cur_n_n_c *cur_n_n_t;

//-----------------------------------------------------------------------------
// Define null pointer:
//-----------------------------------------------------------------------------

#define CUR_N_N_NULL (static_cast<cur_n_n_t>(0))

//=============================================================================
// End of Include File:
//=============================================================================

#endif