Question

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Circular definition in C

typedef struct{
  node *next;
  node *last;
} doubleLink;

typedef struct{
 doubleLink doubleLink;
 int data;
} node;

The above is a doomed attempt to define an object with a double link.
Placing either typedef before the other would draw a compilation error of “unknown type”
One obvious recourse is to change the pointer type specifier in doubleLink to void *
But I wonder whether there are more “harmless” solutions, say, maybe
I can declare the node struct without defining it?

I’m cognizant that this must be a frequently asked question, but I don’t know by what keyword can I possibly find it.

Answer 1

Add forward declacation of node:

struct node;
typedef struct{
  struct node *next;
  struct node *last;
} doubleLink;

As you use pointers, you don’t need to have this type completely defined before the definition of doubleLink.