Question

Have a look at this code snippet:

int i = 10;
int *pi = &i;
int **ppi = π // first declaration
int *api = pi;   // second declaration

printf("i's value is: %d\n",i);
printf("pi's value is: %d\n",*pi);
printf("ppi's value is: %d, at the address: %d\n",**ppi);
printf("api's value is: %d, at the address: %d\n",*api);

Output

$ ./test
i's value is: 10
pi's value is: 10
ppi's value is: 10, at the address: 2686760
api's value is: 10, at the address: 2686760

So which way is (perhaps) more preferrable in those 2 declarations of pointer to pointer, and is there any technical difference between those two?

Answer 1

Technically, you’ve only declared one pointer-to-pointer.

int **ppi = π // first declaration

The second declaration is just a pointer which, when assigned, gets a copy of the first pointer pi‘s address.

Here’s how you can prove it; after your test code, add this:

int i2 = 20;
pi = &i2;

printf("ppi's value is: %d, at the address: %d\n",**ppi,*ppi);
printf("api's value is: %d, at the address: %d\n",*api,api);

The output will be:

ppi's value is: 20, at the address: 2686764 (or some other address)
api's value is: 10, at the address: 2686760

When you change the value of pi (what it points to), dereferencing ppi will reflect the changes, as it points to pi, but because api was just made as a copy of pi before it changed, it will continue pointing to i.