CODEWITHSUNDEEP
cpointers
lord.garbage
lord.garbage

Reputation: 5960

Declare pointer to pointer to pointer

I was trying to understand simple pointers a little better by clarifying for myself the address a pointer points to, the address of the pointer itself and the value the address refers to. So I wrote a small piece of code:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int a;
    int *p;
    int **pp;

    a = 42;

    /* Take the address of a */
    p = &a;

    /* Take the address of p */
    pp = &p;

    printf("Address of int &a:                          %p\n\n", &a);
    printf("value of a:                                 %d\n\n", a);

    printf("Address where *p points to via (void *)p:   %p\n\n", (void *)p);
    printf("Value that *p points to via *p:             %d\n\n", *p);
    printf("Address of *p itself via (void *)&p:        %p\n\n", (void *)&p);

    printf("Address where **p points to via (void *)pp: %p\n\n", (void *)pp);
    printf("Value that **pp points to via **pp:         %d\n\n", **pp);
    printf("Address of **p itself via (void *)&pp:      %p\n\n", (void *)&pp);
    return EXIT_SUCCESS;
}

This all works as expected (Please, do correct me if I made any mistakes here.). Now, I want to go one level deeper and use a pointer to a pointer to pointer ***ppp and assign it the address the pointer to pointer pp points to which is the address *p points to which is the address of a. Here is how I thought I could do it:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int a;
    int *p;
    int **pp;
    int **ppp;

    a = 42;

    /* Take the address of a */
    p = &a;

    /* Take the address of p */
    pp = &p;

    ppp = &pp;

    printf("Address of int &a:                               %p\n\n", &a);
    printf("value of a:                                      %d\n\n", a);

    printf("Address where *p points to via (void *)p:        %p\n\n", (void *)p);
    printf("Value that *p points to via *p:                  %d\n\n", *p);
    printf("Address of *p itself via (void *)&p:             %p\n\n", (void *)&p);

    printf("Address where **pp points to via (void *)pp:     %p\n\n", (void *)pp);
    printf("Value that **pp points to via **pp:              %d\n\n", **pp);
    printf("Address of **pp itself via (void *)&pp:          %p\n\n", (void *)&pp);

    printf("Address where ***ppp points to via (void *)ppp:  %p\n\n", (void *)ppp); 
    printf("Value that ***ppp points to via ***ppp:          %d\n\n", ***ppp);
    printf("Address where ***ppp points to via (void *)&ppp: %p\n\n", (void *)&ppp);

    return EXIT_SUCCESS;
}

But this gives me an incompatible pointer warning. Could someone explain to me why this does not work and if the calls to printf() are right?

Upvotes: 1

Views: 98

Answers (2)

laurisvr
laurisvr

Reputation: 2822

The problem is here:

int **ppp;

That should be 

int ***ppp;

As it is now your trying to force a triple pointer, into a double pointer. Which will probably gives you an error on this line:

ppp = &pp;

Also you might want to have a look at number 2 of this article:).

P.s. For future reference, if you provide a line number and specific error. People might want to help you even better and more:)

Upvotes: 2

Rodrigo FC
Rodrigo FC

Reputation: 31

The error is in this line int **ppp; /* It should be ***ppp, because you're pointing to a pointer which points to another one*/

Upvotes: 3

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