typedef struct and pointer

Question

When we have:

      struct node{.....}
      typedef struct node Node;
      typedef Node *ptr;

is ptr a pointer to struct node or typedef changes the meaning of it?

i have seen typedef on pointers a couple of times and i cant understand how to use it — mojo, May 20 '18 at 05:31
@mojo Pretty sure you meant `typedef Node *ptr`. C is case-sensitive, so `node` is not the same as `Node`. — user3386109, May 20 '18 at 05:39

score 4 · Accepted Answer · edited May 20 '18 at 05:43

The definition

typedef struct node *ptr;

will make ptr an alias for struct node *.

Afterwards you can do either

struct node *some_pointer;

Or

ptr some_pointer;

Both will define the variable some_pointer to be a pointer to the node structure.

But making type-aliases of pointer types is not something I recommend. It can make the code harder to read, understand and maintain.

Take for example the most common problem that I've seen here on Stack Overflow when it comes to pointer type aliases:

ptr some_pointer = malloc(sizeof(ptr));

That allocates memory enough for a pointer to the structure, not for the whole structure. If using e.g.

Node *some_pointer = malloc(sizeof(Node*));

that error would be much clearer and easier to find.

1 Answers1