Using typedef with pointers in C

Question

I am learning at the moment about pointers and lists. I had one question about the typedef keyword.

typedef int data;
typedef struct nodo *lista;
struct nodo {
  data el;
  struct nodo *next;
};

If I write down:

lista l;

Is l a pointer or a struct type. I want to know the part typedef struct nodo *lista; defines lista to be a pointer of struct type or a struct?

Never typedef pointers. You are only making it easier to make mistakes that way. Maybe the only real reason to do that is maybe function pointers. — Fredrik, Nov 26 '19 at 10:35
I would like to know what does the second line of code make. — , Nov 26 '19 at 10:36
`lista l;` is the same thing as `struct nodo *l;`. Now which one is easier to understand? In the first case you don't know if `l` is a pointer or not, in the second case you know. — Jabberwocky, Nov 26 '19 at 11:05
It's curious that the structure definition doesn't use `lista` in place of `struct nodo *`. Not precisely wrong, but a little unexpected. — Jonathan Leffler, Nov 26 '19 at 11:39

score 3 · Answer 1 · answered Nov 26 '19 at 10:37

3

After

typedef struct nodo *lista;

lista is another name for struct nodo *.

So lista l; is the same as struct nodo *l;.

answered Nov 26 '19 at 10:37

user253751

score 1 · Answer 2 · answered Nov 26 '19 at 10:36

1

It defines lista as a pointer to a struct nodo, because of the *.

If it were instead defined as:

typedef struct nodo lista;

lista would be just a struct.

answered Nov 26 '19 at 10:36

legoscia

score 0 · Answer 3 · answered Nov 26 '19 at 10:39

Remove the keyword typedef and you will get a declaration of a pointer to an obejhct of the type struct nodo.

struct nodo *lista;

When the keyword typedef is used

typedef struct nodo *lista;

then instead of declaring an object of the type struct nodo * you are introducing an alias for the type struct nodo *.

So instead of writing for example

struct nodo *head;

you can write

lista head;

3 Answers3