Each .h file requires a struct defined in the other? (C)

Question

I've got two header files, each requiring a type defined in the other. When I try to compile, I get an error regarding an unknown type name. (If I provide only struct declarations and not definitions, I get an incomplete-types error.) What's a solution that will let me share these structs properly?

Right now, my code looks rather like the following (just imagine the #ifndef preprocessor directives etc.):

<headerA.h>

#include "headerB.h"
typedef struct { 
  mytypeB myB;
} mytypeA;

<headerB.h>

#include "headerA.h"
typedef struct {} mytypeB;
void foo( mytypeA * myA);

score 5 · Accepted Answer · answered Mar 05 '12 at 04:01

You should forward-declare the struct mytypeA instead of including headerA.h:

Inside headerB.h:

struct mytypeA; // <<<--- Forward declaration

void foo(struct mytypeA* myA);

This works because you are not using the actual mytypeA, only a pointer to it. You cannot pull the same trick with headerA, because mytypeA includes the actual mytypeB.

score 1 · Answer 2 · answered Mar 05 '12 at 04:03

1

You can forward declare a structure without needing to define the whole thing.

answered Mar 05 '12 at 04:03

Carl Norum

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score 0 · Answer 3 · edited May 23 '17 at 11:48

0

These SO questions might help you since it is related to your question.

undefined C struct forward declaration

How to declare a structure in a header that is to be used by multiple files in c?

edited May 23 '17 at 11:48

Community

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answered Mar 05 '12 at 04:05

minus

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Each .h file requires a struct defined in the other? (C)

3 Answers3