What does the declaration void** mean in the C language?

Question

I'm beginning to learn C and read following code:

public void** list_to_array(List* thiz){
    int size = list_size(thiz);
    void **array = malloc2(sizeof(void *) * size);
    int i=0;
    list_rewind(thiz);
    for(i=0; i<size; i++){
        array[i] = list_next(thiz);
    }
    list_rewind(thiz);
    return array;
}

I don't understand the meaning of void**. Could someone explain it with some examples?

Answer 1

void** is a pointer to a pointer to void (unspecified type). It means that the variable (memory location) contains an address to a memory location, that contains an address to another memory location, and what is stored there is not specified. In this question's case it is a pointer to an array of void* pointers.

Sidenote: A void pointer can't be dereferenced, but a void** can.

void *a[100];
void **aa = a;

By doing this one should be able to do e.g. aa[17] to get at the 18th element of the array a.

To understand such declarations you can use this tool and might as well check a related question or two.