I don't understand structures

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I've got a problem understanding this syntax:

C++

#include <stdio.h>
 
struct point {
    int value;
};
 
int main()
{ 
    struct point s;
   
    // Initialization of the structure pointer
    struct point* ptr = &s;
 
    return 0;
}

And why when I write: scanf("%d", &ptr->value); then I overwrite the value? I also know that &ptr->value is equivalent to ptr.value. I am a bit puzzled because ptr contains the address of the structure s then why can I put value in ptr when it is the address? Should I be able to put value into *ptr instead I put value in ptr?

What I have tried:

It is a bit conflicting when I compare to normal pointers in which *ptr = &x and to change the value of x, I use *ptr and not ptr.

I belive that I don't say something stupid because I compare it to the basic concept of pointer but maybe it works differently to the normal pointers ;>

Posted 30-Oct-23 10:19am

Member 16116753

Updated 4-Nov-23 23:55pm

Deeksha Shenoy

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Richard MacCutchan 1-Nov-23 4:32am

This is your fifth question on the subject, and it would appear that you still do not understand pointers.

Member 16116753 4-Nov-23 13:43pm

I've understood the solution below so please stop sticking pins in my questions. If me trying is a problem then why I can't ask ? It's like that if I want to try understand something I see that it is a problem and points out my inability. Thank you ...

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CPallini · Accepted Answer · 2023-10-30T11:37:00

Yes, when you write

C

scanf("%d", &ptr->value);

if the scanf function call succeed then s.value is changed.

No, &ptr->value is not equivalent to ptr.value.

As matter of fact, ptr->value is equivalent to (*ptr).value, hence you might write

C

&((*ptr).value)

instead of

C

&(ptr->value)

(outer brackets added for clarity).

Try

C

#include <stdio.h>
struct point
{
  int value;
};



int main()
{
  struct point pnt;

  struct point * p = &pnt;

  pnt.value = 0;
  printf("%d\n", pnt.value);

  p->value = 42;
  printf("%d\n", pnt.value);

  (*p).value = -273;
  printf("%d\n", pnt.value);


  scanf("%d", &(p->value));
  printf("%d\n", pnt.value);


  scanf("%d", &((*p).value));
  printf("%d\n", pnt.value);

  return 0;
}