Dynamic array allocated in another function

Question

I am trying to understand how dynamic memory works in C. Suppose I need to allocate memory for some pointer using another function. Is it possible? I tried in the program below, but it keeps crashing in Windows.

void foo(int** x){
    *x=(int *)malloc(10*sizeof(int));
    int i;
    for(i=0; i<10; i++){
        *x[i] = 0;
    }
}

int main(int argc, char* argv[]){

    int *x;
    int i;
    foo(&x);
    for(i=0; i<10; i++){
        printf("%d\n",x[i]);
    }
    return 0;

}

Answer 1

The problem is with this line.

*x[i] = 0;

Add parenthesis to the pointer dereference.

(*x)[i] = 0;

This is because x[i] actually means *(x+i). That is, add i to pointer x to get a new pointer and get the value of that memory location.

Now remember that x is a pointer to a pointer. *x[i] can be more readily be read as **(x+i) when actually you want *((*x)+i).

It might take a bit of thought to get your head around but pointers are easy once you get the hang of it.