compilation error when attempting to set struct pointer

[cs32]

I've run into a bit of a snag with the following code that is perhaps a result of me not fully understanding how to deal with pointers in a struct.

typedef struct {
  int value;
  struct nodeT *next;
} nodeT;

int
main(int argc, char* argv[]) {

  nodeT *node = malloc(sizeof(nodeT));
  nodeT *next = malloc(sizeof(nodeT));

  node->value = 5;
  node->next = next;

  return 0;

}

When I compile, I get the following error:

program.c: In function 'main':
program.c:17: warning: assignment from incompatible pointer type

(this is the line highlighted and bolded in red above)

What am I missing?

Thanks!

[laserlight]

I think the problem is that the struct is unnamed, so struct nodeT is a type unknown at the point where it is used to declare the next member pointer. You should be able to use nodeT as the name of the struct, and then keep the typedef to nodeT.

By the way, you should #include <stdlib.h> for malloc.

[vart]

something like this:

typedef struct nodeT nodeT;

struct nodeT {
  int value;
  nodeT *next;
} ;

[cs32]

OK. This is what I have (headers intentionally excluded). Same compile error.

typedef struct nodeT node;

typedef struct {
  int value;
  node *next;
} nodeT;

int
main(int argc, char* argv[]) {

  nodeT *node = malloc(sizeof(nodeT));
  nodeT *next = malloc(sizeof(nodeT));

  node->value = 5;
  node->next = next;

  return 0;

}

Maybe I'm not understanding this correctly. What's the difference between declaring a struct in the following manners:

typedef struct {
  ...
} nodeT;

typedef struct Node {
  ...
} nodeT;

and

struct Node {
  ...
}

[whiteflags]

No, make an effort to name all your structs that are self-referring. struct { ... is anonymous, and can't have a pointer to itself as a data member.

Like this:

struct node_tag {
   int value;
   struct node_tag * next;
};

typedef struct node_tag NodeT;

I've typically been of the opinion that merging struct declaration and typedef's together are an obtuse exercise. It will work if you name it in the intermediary stage though, before it's named a new type.

[laserlight]

I suggest using:

typedef struct nodeT {
  int value;
  struct nodeT *next;
} nodeT;

What's the difference between declaring a struct in the following manners:

The first defines an unnamed struct. A typedef allows you to use nodeT as the name of the struct, but only after the struct's definition, not within it.

The second defines a struct named Node, but you must use struct Node as the name of the struct. However, a typdef allows you to use nodeT as the name of the struct, instead of struct Node, but only after the struct's definition, not within it.

The third defines a struct name Node, but you must use struct Node as its name.