C recursive header file inclusion problem?

Question

Suppose you have to related structures defined in 2 header files like below:

a.h contents:

#include b.h

typedef struct A
{
  B *b;
} A;

b.h contents:

#include a.h

typedef struct B
{
  A *a;
} B;

In such this case, this recursive inclusion is a problem, but 2 structures must point to other structure, how to accomplish this?

Answer 1

Google C/C++ guidelines suggests:

Don't use an #include when a forward declaration would suffice

That'd mean:

a.h contents:

typedef struct B B;

typedef struct A
{
  B *b;
} A;

b.h contents:

typedef struct A A;

typedef struct B
{
  A *a;
} B;

---

If you prefer something a bit safer (but longer to compile) you can do this:

a.h contents:

#pragma once
typedef struct A A;

#include "B.h"

typedef struct A
{
  B *b;
} A;

b.h contents:

#pragma once
typedef struct B B;

#include "A.h"

typedef struct B
{
  A *a;
} B;