在结构定义中初始化结构成员时出错

Question

I am trying to create a struct that has 2 pointers of type struct nodo defined above the code. But it gives me the error:

expected ':', ',', ';', '}' or 'attribute' before '=' token lista dati_mappa=NULL;".

Here is the code:

typedef int data;

struct nodo
{
    data elem;
    struct nodo *next;
};
typedef struct nodo *lista;

struct mappa {
    data R;
    data C;
    lista dati_mappa = NULL;
    lista pos_valida = NULL;
};

Answer 1

You're not allowed to have inline initialization of structure members in C.

If you want to initialize members then you need to do it after you create instances of the structures.

Answer 2

You can't do that at declaration level in C (in C++ you can).

You need something like this:

...
int main()
{
  struct mappa mymap;
  mymap.dati_mappa = NULL;
  mymap.pos_valida = NULL;
  ...
}

or you can use aggragate initialization:

...
int main()
{
  struct mappa mymap = { .dati_mappa = NULL, 
                         .pos_valida = NULL };
  ...