Unhandled exception trying to set constructor to 0 - c++

Question

I am receiving an unhandled exception when I try to set constructor array to zero. I think the issue is with the constructor, but I am not sure. I chopped out the unnecessary code and reproduced the error. Thanks for the feedback.

The error says: Unhandled exception at 0x0fa4025: Access violation writing location 0x0000.

source:

#include <iostream>
#include <vector>
#include "header.h"
using namespace std;

foo::foo(int b[3][3])
{
    memset(b, 0, sizeof b);
}
void foo::makeMove()
{
    board[1][1] = 1;
}
void foo::print()
{
    for (int i = 0; i < 2; i++){
        for (int j = 0; j < 2; j++){
            cout << board[i][j];
        }

    }
}

header:

class foo
{
public:
    foo::foo(int[3][3] = 0);
    void makeMove();
    void print();

private:
    int board[3][3];
};

main:

#include "header.h" // include definition of class TicTacToe

int main()
{
    foo g; // creates object g of class TicTacToe 
    g.makeMove(); // invokes function makeMove
    g.print();
} //

end main

Answer 1

foo::foo(int[3][3] = 0);

The default value for the argument, which is a pointer, not an array, has been set to 0 . It is invalid when no arguments are passed to the constructor. As such, this is not a reasonable default.

You then write to it via memset , which invokes undefined behavior. I don't even see the point of this design. Why are you taking an external array and setting it to all 0's? Your class has its own array board . Use that.

Next, realize that this is C++ and you are writing your code as if it were C. You have vectors, std::copy , etc.

Answer 2

This happens because to specified default value of the pointer (that points to the array, of course): foo::foo(int[3][3] = 0); . Hence, you are trying to memset 0x0.

Answer 3

Your constructor writes to b without checking if it's 0. You default b to 0, so you invoke undefined behavior.

Add a null check before the memset in the CTOR.

Answer 4

You created an object of class foo

foo g;

using the default constructor with default argument equal to 0.

foo::foo(int[3][3] = 0);

When you tries to access the memory with adrress 0 to fill it

foo::foo(int b[3][3])
{
    memset(b, 0, sizeof b);
}

Also in my opinion this constructor

foo::foo(int b[3][3])
{
    memset(b, 0, sizeof b);
}

has no any sense because it deals with local variable b. I think you wanted to fill data member int board[3][3]; not the local variable.

Answer 5

I think your main mistake is to define a constructor that became the 'default' constructor. This is because you gave it a default value, and so can call it with no arguments. Your loops are also wrong. See below.

#include <iostream>
#include <vector>
#include <memory.h>
using namespace std;

class foo
{
public:
    void makeMove();
    void print();

private:
    int board[3][3] { { 0 }, { 0 }, { 0 } };
};


void foo::makeMove()
{
    board[1][1] = 1;
}
void foo::print()
{
    for (int i = 0; i < 3; i++)
    {
        for (int j = 0; j < 3; j++)
        {
            cout << board[i][j];
        }
        cout << endl;
    }
}

int main()
{
    foo g; // creates object g of class TicTacToe 
    g.makeMove(); // invokes function makeMove
    g.print();
} //

}