Print double pointer to array - keeps crashing

Question

i have this small piece of code which i cant get to work. I am kinda new and i just cant find a mistake i did. Thanks

int main (void)
{
    int **array;
    int i,j, m;

    scanf("%d", &m);

    array = malloc(sizeof(int) * (m*m));


    for (i = 0; i < m; i++) 
    {   
        for (j = 0; j < m; j++) 
        {       
            scanf("%d", &array[i][j]);                     
        }
    }   

        for (i = 0; i < m; i++) 
        {   
            for (j = 0; j < m; j++) 
            {       
                printf("%d", array[i][j]);                  
            }
        }   

    return 0;
}

Check your input! You have m*m+1 scanf's, and not once do you check the result or the return value. — Lee Daniel Crocker
– Lee Daniel Crocker, Commented Nov 20, 2017 at 17:56

user2736738 · Accepted Answer · 2017-11-20 18:16:35Z

What you are allocating is an one dimensional array of size m*m but you are using it as if you have allocated a jagged array where each row contains m elements.

You can allocate a bit different way than what you did

array = malloc(sizeof *array * m);
if( array == NULL)
{
   // error in malloc
}
for(size_t i =0; i<m; i++)
{
   array[i]=  malloc(sizeof *array[i] * m);
   if( array[i] == NULL)
   {
      // error

   }
}
...
for(size_t i = 0; i<m ; i++)
   free(array[i]);
free(array);

Alternatively you can put all the elements in a linear manner using i and j.

int *array;
...
for (i = 0; i < m; i++) 
{   
    for (j = 0; j < m; j++) 
    {       
        if( scanf("%d", &array[i*m+j]) != 1){
           // error in getting input.
        }                     
    }
}   
...
free(array);

Same goes with printf also.

Also don't forget to free the memory you have allocated dynamically after you are done working with it.

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