passing 2d array into a function using only pointer and print the value

Question

the result of this program (process 9164) exited with code -1073741819. the program finished and nothing happens.....what should I do to make it run using only pointer without *x[] or x[][2]

#include <iostream>
#include<string>
#include <fstream>
using namespace std;
void sum(int **x) {
    int s = 0;
    for (int i = 0; i < 3; i++)
    {
        for (int j = 0; j < 2; j++)
        {
            cout << *(*(x + i) + j) << " ";
            s += *(*(x + i) + j);
        }
        cout << "\n";
    }
    cout << s;
}
int main() {
    int x[3][2] = { {11,15},{19,28},{5,8} };
    sum((int**)x);
    return 0;
}

A C-style cast like (int**)x can be very dangerous. The compiler won't tell you that x is certainly not an int**. Your code never produces any pointer to pointer to int. — Drew Dormann
– Drew Dormann, Commented Oct 31, 2021 at 17:50

Some programmer dude · Accepted Answer · 2021-10-31 17:56:04Z

Whenever you feel the need to do a C-style cast (like you do with (int**)x) you should take that as a sign you're doing something wrong.

An array of arrays is not the same as a pointer to a pointer.

What happens is that you pass an invalid pointer, and the program will experience undefined behavior and crash.

What should happen is that the array x decay to a pointer to its first element, i.e. plain x is the same as &x[0]. That will be a pointer to an array, with the type int (*)[2] (in the case of x in your question). That is the type you need to use for the function argument:

void sum(int (*x)[2]) { ... }

And call like

sum(x);

You can also generalize to accept any kind of "2D" array, by using template arguments for the dimensions and passing the array by reference:

// For std::size_t
#include <cstdlib>

template<std::size_t A, std::size_t B>
void sum(int (&x)[A][B])
{
    // Use A and B as the sizes for the arrays...
    ...
}

While the above template version is better, the "proper" solution in C++ should be using std::array, as in:

std::array<std::array<int, 2>, 3> = { ... };

and then pass it as a constant reference to the function.

If the sizes aren't known at compile-time, or if the arrays should be dynamic, then use std::vector instead.

A good book and and good teacher would teach these classes before going into pointers or C-style arrays.

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