Dereferencing pointer to incomplete type

Question

I am getting the following error from this piece of code, I am new to C and learning as I go along!

cc -g -I /usr/lib/i386-linux-gnu -c anld.c
anld.c: In function ‘main’:
anld.c:379:11: error: dereferencing pointer to incomplete type

Main .C file

bridge_t *bridge_p = bridge_new();   //Create / init our bridge

bridge_p->s = server_connect(options.server_p, options.dest_port,
            options.ifname_p, options.gateway_p);

bridge .C file

struct bridge
{
  int s;
};

bridge_t *bridge_new(void)
{
  bridge_t *bridge_p;

  bridge_p = OPENSSL_malloc(sizeof *bridge_p);
  if (!bridge_p)
  {
    return NULL;
  }

  /* Initialise bridge */
  memset(bridge_p, '\0', sizeof *bridge_p);

  bridge_p->s = -1;

  return bridge_p;
}

bridge.h file

typedef struct bridge bridge_t;

Anybody have any ideas??

Answer 1

To avoid the error you mention you should move this:

struct bridge
{
  int s;
};

to bridge.h.

Currently it is declared local to the module (translation unit) bridge.c and so its members are not know to the outside world.

---

Alternativly, if you want to hide the internals of struct bridge, you need to add a getter and a setter function to the module bridge.c for each member which you want to access from the outside like for example so:

bridge.h

typedef struct bridge bridge_t;

void brigde_s_set(bridge_t *, int);
int bridge_s_get(bridge_t *);

bridge.c

#include "bridge.h"

struct bridge
{
  int s;   
};

int brigde_s_set(bridge_t * pb, int s)
{
  pb->s = s;
}

int bridge_s_get(bridge_t * pb)
{
  return pb->s;
}

So the snippet from your main.c would then look like:

#include "bridge.h"

...

bridge_t * bridge_p = bridge_new();   //Create / init our bridge

bridge_s_set(bridge_p, 
  server_connect(options.server_p, options.dest_port, options.ifname_p, options.gateway_p));