CODEWITHSUNDEEP
c++c++11c++14
Z4ckZ3r0
Z4ckZ3r0

Reputation: 113

std::shared_ptr not updating its count

I am trying to create a network of a custom class Tile inside another class Board which is storing a std::array<std::shared_ptr<Tile>, 34>. I am using std::shared_ptr<Tile> objects within class Tile to show which nodes are connected. However, when I initialise each of the 34 Tile objects, the not yet initialised objects included in the list do not get updated from nullptr to their own reference.

#include <memory>
#include <array>
#include <cstddef>

struct Tile;
template <const std::size_t N> using TileLink  = std::array<const std::shared_ptr<const Tile>, N>;
template <const std::size_t N> using TileArray = std::array<std::shared_ptr<const Tile>, N>;

struct Tile {
    /* surrounding tiles */
    const std::size_t ID;
    const std::size_t num_adj;
    const TileLink<6> adjacent;
    Tile (std::size_t id, std::size_t n, const TileLink<6> & arr) : ID (id), num_adj (n), adjacent (arr) { }
    ~Tile (void) = default;
};

class Board {
private:
    TileArray<34> tiles;
public:
    Board (void);
    ~Board (void) = default;
};

Board :: Board (void) {
    /* Column 1 */
    tiles[0]  = std::make_shared<Tile> ( 0, 3, TileLink<6>{ tiles[1],  tiles[4],  tiles[5],  nullptr,   nullptr,   nullptr   });
    tiles[1]  = std::make_shared<Tile> ( 1, 4, TileLink<6>{ tiles[0],  tiles[2],  tiles[5],  tiles[6],  nullptr,   nullptr   });
    tiles[2]  = std::make_shared<Tile> ( 2, 3, TileLink<6>{ tiles[1],  tiles[6],  tiles[7],  nullptr,   nullptr,   nullptr   });
    /* Column 2 */
    tiles[3]  = std::make_shared<Tile> ( 3, 2, TileLink<6>{ tiles[4],  tiles[9],  nullptr,   nullptr,   nullptr,   nullptr   });
    tiles[4]  = std::make_shared<Tile> ( 4, 5, TileLink<6>{ tiles[0],  tiles[3],  tiles[5],  tiles[9],  tiles[10], nullptr   });
    tiles[5]  = std::make_shared<Tile> ( 5, 6, TileLink<6>{ tiles[0],  tiles[1],  tiles[4],  tiles[6],  tiles[10], tiles[11] });
    tiles[6]  = std::make_shared<Tile> ( 6, 6, TileLink<6>{ tiles[1],  tiles[2],  tiles[5],  tiles[7],  tiles[11], tiles[12] });
    tiles[7]  = std::make_shared<Tile> ( 7, 5, TileLink<6>{ tiles[2],  tiles[6],  tiles[8],  tiles[12], tiles[13], nullptr   });
    tiles[8]  = std::make_shared<Tile> ( 8, 2, TileLink<6>{ tiles[7],  tiles[13], nullptr,   nullptr,   nullptr,   nullptr   });
    /* Columns 4 - 6 */
    ...
    ...
    ...
    /* Column 7 */
    tiles[31] = std::make_shared<Tile> (31, 3, TileLink<6>{ tiles[26], tiles[27], tiles[32], nullptr,   nullptr,   nullptr   });
    tiles[32] = std::make_shared<Tile> (32, 4, TileLink<6>{ tiles[27], tiles[28], tiles[31], tiles[33], nullptr,   nullptr   });
    tiles[33] = std::make_shared<Tile> (33, 3, TileLink<6>{ tiles[28], tiles[29], tiles[32], nullptr,   nullptr,   nullptr   });
}

The std::array I am passing to the Tile constructor does not change. How would I get it to change?

Any help would be greatly appreciated. Sorry for making the question so long, I didn't really know how to make this a smaller example.

Upvotes: 0

Views: 129

Answers (2)

Z4ckZ3r0
Z4ckZ3r0

Reputation: 113

I have solved my problem - thanks to @t.niese and @fjardon for your help.

I had to make Tile more complex to facilitate the real issue here: that I was unable to create a unique Tile object from std::array in the class. So I added a copy constructor and an assignment operator, removed the smart pointers and the const-ness and made the array of class type Tile.

class Tile;
template <const std::size_t N> using TileLink  = std::array<const Tile *, N>;
template <const std::size_t N> using TileArray = std::array<Tile, N>;

enum class OWNERSHIP { PLAYER_1, PLAYER_2, CONTESTED };

class Tile {
private:
    OWNERSHIP territory;
    /* surrounding tiles */
    std::size_t ID;
    std::size_t num_adj;
    TileLink<6> adjacent = { nullptr };
public:
    Tile (void) { }
    Tile (OWNERSHIP own, std::size_t id, std::size_t num, const TileLink<6> & arr);
    Tile (const Tile & rhs);
    Tile & operator = (Tile other);
    ~Tile (void) = default;
};

class Board {
private:
    TileArray<34> tiles;
    void create_col_1_and_7 (void);
    void create_col_2 (void);
    ...
    void create_col_6 (void);
public:
    Board (void);
    ~Board (void) = default;
};

Each of the initialisation now looks like:

tiles[0]  = Tile (OWNERSHIP::PLAYER_2,   0, 3, TileLink<6>{ &tiles[1],  &tiles[4],  &tiles[5],  nullptr,    nullptr,    nullptr    });
tiles[1]  = Tile (OWNERSHIP::CONTESTED,  1, 4, TileLink<6>{ &tiles[0],  &tiles[2],  &tiles[5],  &tiles[6],  nullptr,    nullptr    });
...
tiles[32] = Tile (OWNERSHIP::CONTESTED, 32, 4, TileLink<6>{ &tiles[27], &tiles[28], &tiles[31], &tiles[33], nullptr,    nullptr    });
tiles[33] = Tile (OWNERSHIP::PLAYER_1,  33, 3, TileLink<6>{ &tiles[28], &tiles[29], &tiles[32], nullptr,    nullptr,    nullptr    });

Upvotes: 0

fjardon
fjardon

Reputation: 7996

Here:

tiles[0]  = std::make_shared<Tile> ( 0, 3, TileLink<6>{ tiles[1],  tiles[4],  tiles[5],  nullptr,   nullptr,   nullptr   });

tiles[1], tiles[4], and so on, are not yet initialized and are shared_ptr to nullptr. When you initialize tiles[1] later it doesn't change what is inside tiles[0].

You are completely misusing shared_ptr. Since your tile array has a fixed size, just allocate once all the needed memory and then use non-owning pointers. Because there is a owner for the memory and it is Board.

Upvotes: 2

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