When to use **ptr, practical example?

Question

Can anyone describe when exactly is the pointer to a pointer variable is used with a practical example plz? It would be much appreciated. Tnx in advance!

Answer 1

A list is just a pointer right?
Like, a string is a list of characters, or char*.
So your shopping list, a list of strings, is char**.
If you are keeping all shopping lists you ever wrote in a folder, that's a char***.

Also. You use pointers so functions can change the variables you pass in, right?

void change_value(int* p){ *p += 2; }

int x = 0;
change_value(&x); // x is now 2.

Similarly you can use a pointer to a pointer to change a pointer of your choice!

void change_ptr(char** p){ *p += 2; }

char* p = "hello world!";
change_ptr(&p); // p now points to "llo world!"

Pointer pointers may seem hard and useless if you're not used to them, but I guarantee that one day you'll be working on a problem and pointer pointers will be the solution, and it will be obvious and you'll exactly know what to do :)
At the end of the day a pointer pointer is like any other pointer.

Answer 2

Great explanation. You're awesome! Thanks a lot.