can we have a double function pointer in C?-CodePudding

I am wondering that unlike the double pointers (int**) , can we have double function pointer?

I mean the function pointer pointing to the address of the another function pointer ?

I want something like

int add(int A , int B){
    return A B;
}

int main(void){

    int (*funcpointerToAdd)(int,int) = add; // single function pointer pointing to the function add
    printf("%d \n",funcpointerToAdd(2,3));
  

    int (**doubleFuncPointerToAdd)(int,int) = &funcpointerToAdd;
    printf("%d \n",doubleFuncPointerToAdd(2,3));

    return 0;
}

but this gives me an error called object ‘doubleFuncPointerToAdd’ is not a function or function pointer

is this possible to do this thing anyway ?

CodePudding user response：

You can use pointers to pointers to functions, but you have to deference them once first:

int add(int A , int B){
    return A B;
}

int main(void){

    int (*funcpointerToAdd)(int,int) = &add;
//By the way, it is a POINTER to a function, so you need to add the ampersand
//to get its location in memory. In c   it is implied for functions, but
//you should still use it.
    printf("%d \n",funcpointerToAdd(2,3));
  

    int (**doubleFuncPointerToAdd)(int,int) = &funcpointerToAdd;
    printf("%d \n",(*doubleFuncPointerToAdd)(2,3));
//You need to dereference the double pointer,
//to turn it into a normal pointer, which you can then call

    return 0;
}

This is also true for other types:

struct whatever {
   int a;
};

int main() {
   whatever s;
   s.a = 15;
   printf("%d\n",s.a);
   whatever* p1 = &s;
   printf("%d\n",p1->a); //OK
//x->y is just a shortcut for (*x).y
   whatever** p2 = &p1;
   printf("%d\n",p2->a); //ERROR, trying to get value (*p2).a,
//which is a double pointer, so it's equivalent to p1.a
   printf("%d\n",(*p2)->a); //OK
}