include - C circular dependency

Question

I have this problem with circular dependency in C, I looked around the other questions about this topic but really couldn't find the answer.

I have this first struct named vertex:

#ifndef MapTest_vertex_h
#define MapTest_vertex_h

#include "edgelist.h" //includes edgelist because it's needed

typedef struct 
{
    char* name;
    float x, y;
    edgelist* edges;
} vertex;

#endif

The second struct is the edgelist which is included by the vertex.

#ifndef edgelist_h
#define edgelist_h

#include "edge.h" //include edge, because its needed

typedef struct _edgelist
{
    edge** edges; 
    int capacity, size;
} edgelist;

//...

#endif

And then the last struct, the one where the problem raises, the edge struct gets included by the edgelist above.

#ifndef MapTest_edge_h
#define MapTest_edge_h

#include "vertex.h" //needs to be included because it will be unkown otherwise

typedef struct 
{
    float weight;
    vertex* destination;
    int found; 
} edge;

#endif

I tried everything I could, forward declaring, using #ifndef, #define etc. but couldn't find the answer.

How can I resolve this circular dependency problem?

Answer 1

Seems like you shouldn't need to include anything in any of the files. A forward declaration of the relevant types should be sufficient:

#ifndef MapTest_vertex_h
#define MapTest_vertex_h

struct edgelist;

typedef struct
{
    char* name;
    float x, y;
    edgelist* edges;    // C++ only - not C
} vertex;

#endif

etc. In C coding, you have to write:

struct edgelist;

typedef struct
{
    char* name;
    float x, y;
    struct edgelist* edges;
} vertex;