Question

I wrote a simple program to test array pointer:

    #include <iostream>

    using namespace std;

    int main(){
        int (*array)[10];
        int i, j;
        for (i = 0; i < 10; i++){
            for (j = 0; j < 10; j++)
                array[i][j] = 1;
        }
        for (i = 0; i < 10; i++){
            for (j = 0; j < 10; j++)
                cout << array[i][j] << " ";
            cout << endl;
        }
        return 0;
    }

why the g++ “Segmentation fault”?
by the way, my os is ios x64.

Thanks
Chuan

Answer 1

array is a pointer to an array, which you apparently already know. However, you never allocated memory for the actual array, i.e. your pointer is pointing “nowhere”. You are trying to access something that does not exist, which often leads to segmentation fault.

For example, you can declare an actual array

int array10x10[10][10];

and make your pointer point to it

array = array10x10;

(more precisely, your pointer is now pointing to the first 10-element subarray in array10x10). After that your code will work fine, meaning that by accessing array[i][j] you will indirectly access array10x10[i][j].

Alternatively you can allocate the actual array in dynamic memory, if you so desire

array = new int[10][10];

(just don’t forget to do a delete[] array at the end).