Question

A.h

#ifndef A
#define A

#include "B.h"

typedef struct {
    B* b;
} A;
void InitA(A* a) {
    a->b=malloc(sizeof(B));
}

#endif

B.h

#ifndef B
#define B

#include "A.h"

typedef struct {
    A* a;
} B;
void InitB(B* b) {
    b->a=malloc(sizeof(A));
}

#endif

I tried like that ,like c++ and typedef.
typedef makes conflict errors between types and previous declare was here and etc.

Thanks.

Answer 1

Here’s one way of fixing it:

a.h:

#ifndef A_H_
#define A_H_

typedef struct A
{
  struct B* b;
} A;

#include "b.h"

void InitA(A* a)
{
  a->b = malloc(sizeof(B));
}

#endif

b.h:

#ifndef B_H_
#define B_H_

typedef struct B
{
  struct A* a;
} B;

#include "a.h"

void InitB(B* b)
{
  b->a = malloc(sizeof(A));
}

#endif

main.c:

#include <stdlib.h>
#include "a.h"
#include "b.h"

int main(void)
{
  A a;
  B b;
  InitA(&a);
  InitB(&b);
  return 0;
}

The problem is, for sizeof() to work, its parameter must be of a known type. In your code A and B are not yet fully known when you do sizeof(A) and sizeof(B) in InitA() and InitB(). Rearranging the order of the type definitions, file inclusion and the function definitions can fix that.