CODEWITHSUNDEEP
c++classmemory-managementdynamic
Viktor Apoyan
Viktor Apoyan

Reputation: 10755

Dynamic allocated class object

I have simple class which you can see below:

Questions

  1. Can I have in my Playground class constructor like this Playground(int aRow, int aColumn); If YES how I must allocate memory in then case for elements of row and column ? If NO why ?
  2. Why I can't write mPlayground[0][0] = 0 and what can I do to do that ? If I can of course.

Playboard.h

#pragma once
#ifndef PLAYBOARD_H
#define PLAYBOARD_H

class Playground
{
public:
    Playground()
    {       
    }
};

class Playboard
{
public:
    Playboard();
    ~Playboard();

private:
    Playground** mPlayground;
    int mRows;
    int mColumns;

public:
    void Initialize(int aRow, int aColumn);
};

#endif /** PLAYBOARD_H */

Playboard.cpp

#include "Playboard.h"
Playboard::Playboard()
{
    mPlayground = 0;
}

void Playboard::Initialize(int aRow, int aColumn)
{
    // Set rows and columns in order to use them  in future.
    mRows = aRow;
    mColumns = aColumn;

    // Memory allocated for elements of rows.
    mPlayground = new Playground*[aRow];
    // Memory allocated for elements of each column.
    for (int i=0; i<aRow; i++)
        mPlayground[i] = new Playground[aColumn];
}

Playboard::~Playboard()
{
    // Free the allocated memory
    for (int i=0; i<mRows; i++)
        delete[] mPlayground[i];
    delete[] mPlayground;
}

Upvotes: 0

Views: 2045

Answers (2)

Robᵩ
Robᵩ

Reputation: 168876

1a Can I have in my Playground class constructor like this Playground(int aRow, int aColumn);

Yes, trivially:

class Playground {
    int x, y;
    Playgrown(int aX, int xY) : x(aX), y(aY) {}
};

1b If YES how I must allocate memory in then case for elements of row and column ? If NO why ?

You don't have to allocate memory at all. Playground contains no pointers, and consequently requires no allocation.

2 Why I can't write mPlayground[0][0] = 0 and what can I do to do that ? If I can of course.

Because you haven't overloaded the assignment operator for Playground. For example,

class Playground {
    …
    // Sample operator=. You'll need to implement its semantics
    void operator=(int) {}
};

You cannot initialize members of the array with new. You might be able to do this:

{
    mPlayground[i] = new Playground[aColumn];
    for(int x = 0; x < i; x++)
      mPlayground[i][x] = Playground(3,4);
}

Upvotes: 2

Luchian Grigore
Luchian Grigore

Reputation: 258678

1) Yes:

Playground(int aRow, int aColumn)
{
}

2) EDIT: Sorry I thought it was a more complicated matter. I'll leave the below answer here for future reference. To be able to write mPlayground[0][0] = 0, you'll need to overload 

Playground& Playground::operator = ( int x );

Old answer:

To be able to access Playground objects from the Playboard class, you can overload the () operator and call:

Playground Playboard::operator()(int r, int c)
{
    return mPlayground[r][c];
}

//...
Playboard p;
p(x,y);

or the [] operator:

Playground* Playboard::operator[] (int r)
{
    return mPlayground[r];
}

 //...
 Playboard p;
 p[x][y];

Upvotes: 1

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