Simple C double pointer

Question

I am learning C pointers and quite confused. I tried to search online but couldn't find any clear explanation. This is what I am trying to understand:

int x = 8;
int *ptr = &x;
int **dptr = ptr;

What does **dptr point to, x or *ptr? When I tried to print the content of dptr I found that it contains the address of x instead of *ptr but I am not sure why?

Edited

int x = 8;
int *p = &x;
int **ptr = &p;
int **dptr = ptr;

This shouldn't compile. You can't assign ptr to dptr. One is an int* and one is an int**. — Benjy Kessler
– Benjy Kessler, Commented May 2, 2015 at 18:09

ouah · Accepted Answer · 2015-05-02 18:11:51Z

2

First off, I assume you meant: int **dptr = &ptr; as int **dptr = ptr; is invalid.

int x = 8;
int *ptr = &x;
int **dptr = &ptr;

dptr points to ptr object.

*dptr points to x object.

**dptr is not a pointer but the int object x.

EDIT: question was edited, ptr was an int * but seems to be an int ** now...

edited May 2, 2015 at 18:11

answered May 2, 2015 at 18:09

ouah

147k16 gold badges287 silver badges338 bronze badges

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

4 Comments

Programm-ist Over a year ago

Sorry, I meant int **ptr = &x and int **dptr = ptr.

ouah Over a year ago

@Programm-ist in that case it is invalid C. Did you mean int **dptr = (int **) ptr?

Programm-ist Over a year ago

what about this then? int x = 8, int *p = &x, int **ptr = &p, int **dptr = ptr;

ouah Over a year ago

@Programm-ist then dptr has then the same value as ptr so **dptr is the same as **ptr.

Arun A S · Accepted Answer · 2015-05-02 18:27:19Z

0

int x = 8;
int *p = &x;
int **ptr = &p;
int **dptr = ptr;

First, the value 8 is stored in x.

Next, with the statement

int *p = &x;

p will point to x ( that is , p now stores the address of x )

int **ptr = &p;

Now ptr will store the address of p, which in turn stores the address of x

int **dptr = ptr;

dptr stores the address of ptr which in turn stores the address of p which points to x.

So, Now, **dptr will have the value of the integer x.

edited May 2, 2015 at 18:27

answered May 2, 2015 at 18:11

Arun A S

7,0704 gold badges33 silver badges54 bronze badges

Comments

John Bode · Accepted Answer · 2015-05-04 14:13:17Z

0

Given the declarations

int x = 8;
int *p = &x;
int **ptr = &p;
int **dptr = ptr;

Then the following are true:

**dptr == **ptr == *p ==  x == 8  (int)
 *dptr ==  *ptr ==  p == &x       (int *)
  dptr ==   ptr == &p             (int **)

edited May 4, 2015 at 14:13

answered May 3, 2015 at 2:07

John Bode

125k19 gold badges130 silver badges211 bronze badges

Collectives™ on Stack Overflow

Simple C double pointer

3 Answers 3

4 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

4 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related