CODEWITHSUNDEEP
c++arrays
John Kemp
John Kemp

Reputation: 159

Check if an object in a 2D array is Null

I have a 2Dimensional array, that is supposed to hold objects that are constantly moving.

class ZombieLand : public Singleton<ZombieLand>
{
   DECLARE_SINGLETON(ZombieLand);
public:
    MachineState world [19][19];
    MachineState getWorld()
    {
       std::cout<<"World";
       return world[19][19];
    }
    void setWorld(MachineState & state)
    {
    world [state.x][state.y] = state;

    }
}

I try to check if a certain location is Null, but the "NULL" word does not work, nor does 0

switch (state.m_Facing)
{
 case (MachineState::UP):
    if(ZombieLand::get().world[state.x][state.y-1] != NULL )
    {
       state.m_occupied = true;
       break;
    }

My question is, how can I check to see if a location of my world array already holds an object? Thank you in Advance.

My MachineState class

struct MachineState
{

template <typename MachineTraits>
friend class Machine;

enum Facing { UP, RIGHT, DOWN, LEFT};
MachineState()
    : m_ProgramCounter(1)
    , m_ActionsTaken(0)
    , m_Facing(UP)
    , m_Test(false)
    , m_Memory(nullptr)
    ,x(0)
    ,y(0)
    ,point1(25, 10)
    ,point2(10, 40)
    ,point3(40, 40)

{ }
  int m_ProgramCounter;
  int m_ActionsTaken;
  Facing m_Facing;
  bool m_Test;
  bool m_occupied;
  int x;
  int y;
  Point point1;
  Point point2;
  Point point3;

  int GetActionsPerTurn() const throw() { return m_ActionsPerTurn; }
  int GetMaxMemory() const throw() {return m_MaxMemory; }
  bool GetInfect() const throw() { return m_InfectOnAttack; }
  void setPoint(Point p1, Point p2, Point p3)
  {
    point1=p1;
    point2=p2;
    point3=p3;
 }

};

Upvotes: 0

Views: 2170

Answers (1)

Refugnic Eternium
Refugnic Eternium

Reputation: 4291

There are two ways for you to go here.

First: In your constructor of MachineState you'd have to set a variable, which determines what is on that field and to add a function, which tells you that. If the return value of that is '0' you'll know that the field is empty.

Second: Declare a two dimensional array of pointers.

MachineState *world[19][19];
memset(world, 0, sizeof(world));

This little code will set all the pointers to 0 (NULL), which you can then check. Of course you'd need to allocate objects to this two dimensional array manually then.

As a little plus, your getWorld() function looks rather buggy.

Please consider using this function instead:

MachineState *getField(MachineState state) {
    return world[state.x][state.y];
}

Alternatively, you can of course use:

MachineState *getField(int X, int Y) {
    return world[X][Y];
}

The latter function could be called as:

MachineState *Field = ZombieLand::getField(state.x, state.y - 1);
if(Field != NULL) state.m_occupied = true;

Of course you'd need to add boundary checking, but that's beyond the scope of this answer.

Upvotes: 2

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