modifying a pointer that points to another pointer

Question

Using no other objects besides those already declared, how can you alter ptrptr so that it points at a pointer to b without directly touching ptr ?

int a,b;
int *ptr;
int**ptrptr;

ptr =&a;
ptrptr=&ptr;

What does this have to do with array, vector or resize? Please reduce your tags to just those that describe the problem you are having. — Toby Speight
– Toby Speight, Commented Nov 1, 2016 at 17:29
ops .. sry mate ,i was about to ask something but i have figured it on my own so i deleted it and forgot to remove the tages .. thnx — ahmed elbarky
– ahmed elbarky, Commented Nov 1, 2016 at 18:02

Christophe · Accepted Answer · 2016-11-01 12:05:18Z

2

You're not allowed to touch directly ptr. So ptr = &b; is not an option.

But this doesn't prevent changing it indirectly. So *ptrptr=&b; would be the way to go.

answered Nov 1, 2016 at 12:05

Christophe

75.1k7 gold badges87 silver badges182 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Peter Over a year ago

That is not actually altering (changing) ptrptr. It is changing *ptrptr so it points to b (i.e. contains the address of b), which is a somewhat different from the question asked.

am2 Over a year ago

I think it is the exact answer to this question. How to work with pointers to pointer?

ahmed elbarky Over a year ago

i got the question from a book called Data structure and problem solving by mark Allen .. isnt changing the address normally changes the value assigned to it ?

Christophe Over a year ago

@ahmedelbarky Suppose a=1; and b=2;. None of these pointer statements change the value contained in a or in b. It only changes the pointers themselves. If you print **ptrptr immediately after your code, you'd get 1. If you print **ptrptr after my statement, you'd get 2. But a and b are still unchanged. If after my statement you'd assign **ptrptr=3; then only the content of b would be changed to 3.

Collectives™ on Stack Overflow

modifying a pointer that points to another pointer

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related