Accessing pointer member data of struct

Question

I am trying to access the data of a pointer that is a member of a struct.

typedef struct
{
    int i1;
    int* pi1;
} S;


int main()
{
    S s1 = { 5 , &(s1.i1) };

    printf("%u\n%u\n" , s1.i1 , s1.pi1 ); //here is the problem 

return 0;
}

The problem lies in the second argument of printf. When i run the program i get the following result in console: 5 ...(next line) 2381238723(it's different every time). This is correct, and the result is not unexpected. I have tried things like:

*(s1.pi1)

and

s1.*pi1

None of them works. Is there any operator in C or method to do this?

ask yourself what is the result of the expression `&(s1.pi1)` used to build your structure. Keep in mind that a pointer makes sense if it points to something, a pointer doesn't imply the existence of an associated object. — user2485710, Jan 11 '14 at 19:04
`s1.pi1` _does_ access the "pointer member data of struct". Curiously it appears the value `s1.pi1` is initialized with its address. — chux - Reinstate Monica, Jan 11 '14 at 19:08
Yes i know i typed wrong. Though i still get the same result when i run it. — Eijomjo, Jan 11 '14 at 19:11
It was as you said i think. When i edited the code correctly and used *(s1.pi1) it worked! Sorry this is the second post i mess up. But i am very thankful for your answers! It helped me solve the problem. — Eijomjo, Jan 11 '14 at 19:19

godel9 · Accepted Answer · 2014-01-11T19:22:40.403

3

I'm guessing here, but I think you might have meant to do the following:

typedef struct
{
    int i1;
    int* pi1;
} S;


int main()
{
    // Take the address of s1.i1, not s1.pi1
    S s1 = { 5 , &(s1.i1) };

    // Dereference s1.pi1
    printf("%u\n%u\n" , s1.i1 , *s1.pi1 );

    return 0;
}

edited Jan 11 '14 at 19:22

answered Jan 11 '14 at 19:04

godel9

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Yes, sorry i changed it now. Though i get the same result when i run it – Eijomjo Jan 11 '14 at 19:09
@Eijomjo Did you make the other change, dereferencing `s1.pi1`? – godel9 Jan 11 '14 at 19:20

score 1 · Answer 2 · edited May 23 '17 at 11:51

Going through godel9's suggestion and comments, I infer that you have found a way to get the expected results

You wrote: I have tried things like:

*(s1.pi1) and s1.*pi1

I sense a li'l confusion there.

mystruct.pointer means that you have access to the pointer, now give,take,compare.. address.

*(mystruct.pointer) means that you have dereferenced the pointer,now giv, take,increment.. value.

Remember that pointers are just variables which store addresses(!) but more versatile than the common ones.

Accessing pointer member data of struct

2 Answers2