error: array type has incomplete element type - already defined structs

Question

extern  const   struct  ss_type     ss_table    [MAX_CLASS];
extern  const   struct  ss_group_type   ss_group_table  [MAX_GROUPS];

merc.h:4430:30: error: array type has incomplete element type merc.h:4431:35: error: array type has incomplete element type

Working on a pet project and am completely stumped on this one. I don't really have an idea of why this error would reflect these lines. My best guess would be that the compiler can't make sense of what ss_table, ss_type, ss_group_table, and ss_group_type are.

However, ss_table and ss_type are defined

const struct ss_type    ss_table [MAX_CLASS] =  {   {   /* FALSE */  
"",     
{0},    
{0},    
{NULL}  
},

So are ss_group_table and ss_group_type

const struct ss_group_type  ss_group_table [MAX_GROUPS] = 
{
  /* NONE: FALSE return 0 */
  {"", 0,
   {
     {NULL, 0, 0,   {NULL},    {NULL}  }
   }
  },

which puts me at a loss for how to resolve this error.

Answer 1

No, type has only be forward-declared, but not been specified. At least you didn't give us any. A resl definition like

struct toto {
  double hei;
};

must be visible.

Such struct definitions should be put in a header file .h and be included in .c files (co called compilation units) to make the definitions visible.

Answer 2

If the type is incomplete, it means that the it has been forward-declared, but has not yet been declared fully.

For example, the following compiles:

struct S1 {};
struct S1 arr1[10];

whereas the following doesn't:

struct S2;
struct S2 arr2[10]; /* error: array type has incomplete element type */
struct S2 {};