Struct basics (struct as pointer)

Question

    #include<stdio.h>

    typedef struct
    {
        int *u;
        struct node next;
    } *node;

    int main()
    {
        return 0;
    }

What is meant by *node here? I don't get it. I think there should be a node here but it is compiling anyway.

@KirilKirov since like a month ago. You've missed the message on the right side. There's been some effort to clean up questions with this tag. — Alexey Frunze, Oct 19 '12 at 11:26
@KirilKirov: http://meta.stackexchange.com/questions/147100/the-homework-tag-is-now-officially-deprecated — adripanico, Oct 19 '12 at 11:26
Wow, 3 answers within 14 seconds :) Thanks, I've missed that. — Kiril Kirov, Oct 19 '12 at 11:26

score 2 · Accepted Answer · answered Oct 19 '12 at 11:22

2

Here typedef defines a new type, node, which is a pointer to the structure.

The code in the question may not compile since struct node doesn't appear to be defined anywhere and yet it's used inside of the structure.

answered Oct 19 '12 at 11:22

Alexey Frunze

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score 0 · Answer 2 · answered Oct 19 '12 at 11:24

Compare this:

typedef int * pointer_to_int;

Here, the asterisk is part of the type being given a new name, i.e. pointer_to_int is an alias for the type int *.

With your example, it's exactly the same! The asterisk is part of the type, so that node becomes an alias for the type pointer to struct node { int *u; struct node *next; }.

Also, note that it's often a bad idea to include the asterisk in typedef, since it makes the code much harder to use. In C, it's often very interesting to know whether a variable is a pointer or not, so hiding that fact isn't very helpful.

b3h3m0th · Answer 3 · 2012-10-19T12:00:41.233

0

The correct definition is:

typedef struct Node {
    int *u;
    struct Node *next;
} *node;

In your code there is a problem in a struct declaration; syntax is:

struct identifier/tag {struct declaration list}

struct declaration list is a sequence of declarations for the members of the structure;

typedef declaration provides a way to create an alias, a synonym for the type; syntax is:

typedef type alias

Where is the Error?

typedef struct {

In this case there isn't an alias!

edited Oct 19 '12 at 12:00

answered Oct 19 '12 at 11:24

b3h3m0th

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Any elaboration on what you did and why? – Alexey Frunze Oct 19 '12 at 11:25
@Surai Menon Maybe you are interested into a: http://stackoverflow.com/questions/4481603/creating-typedef-pointers-to-typedef-structs-in-c – b3h3m0th Oct 19 '12 at 11:26
I'm not asking to explain it for myself. It's just to the OP your answer may not be very helpful. – Alexey Frunze Oct 19 '12 at 11:27
it is simply the correct construction of node, what is the problem about that? I don't understand what do you want! – b3h3m0th Oct 19 '12 at 11:30
1

I'm only pointing out that the answer is incomplete and possibly unclear to the OP. – Alexey Frunze Oct 19 '12 at 11:41
I added some info, thanks for the advice. I hope that is correct now. – b3h3m0th Oct 19 '12 at 12:02

score 0 · Answer 4 · answered Oct 19 '12 at 11:26

problems here:

typedef struct
    {
        int *u;
        struct node next; //struct node is NOT defined.
    } *node;

This is wrong:

it should be :

typedef struct node{
   int *u;
   struct node *next;
}*nodeptr;

This code means that "nodeptr" is a pointer to struct node;

score 0 · Answer 5 · answered Oct 19 '12 at 11:29

0

Personally, I've never seen this kind of declaration. This use to be something like:

typedef struct {
  int *u;
  struct node *next;
} node;

And that's simple: you are defining a structure with a pointer to an integer and a pointer to another element of the same structure.

answered Oct 19 '12 at 11:29

adripanico

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In your code, the `struct` is anonymous. Thus field `next` is not a pointer to a similar `struct` but to an undefined `struct node`. The `typedef` has nothing to do with the name of the `struct` itself (`typedef struct { ... } name` is more or less equivalent to `struct __anonymous__ { ... }; typedef struct __anonymous__ name`) – Virgile Oct 19 '12 at 13:00

Struct basics (struct as pointer)

5 Answers5