Self-referential typedef without object or struct

Question

I'm fairly new to c++, and I'm trying to implement a simple trie to store a lexicon of strings, using the std::map or other c++ standard library container classes. What I'd like to be able to do is use something like

typedef (map<char, type_node>)* type_node;

for which clang++ gives me the error ' use of undeclared identifier "type_node" '.

This as opposed to a self-referential structure, such as

typedef struct node {
   int data;
   struct node *next;
} Node;

Which works fine, somehow.

Is it possible to declare self-referential types without using a class or struct?

Why does the structure work and not the recursive alias type?

Is there a better way to do this?

Nope. A typedef is an alias. Aliases cannot be forward-declared. — Sam Varshavchik, Feb 25 '17 at 02:28
Aside: "object orientation" is not a synonym for "used a class/struct". — , Feb 25 '17 at 02:30

score 0 · Accepted Answer · edited May 23 '17 at 12:09

0

You cannot declare containers with incomplete types[1]. So map<char, type_node> is an error and consequently the alias is also an error.

In C++ all structs are implicitly typedef'd[2]. Your structure can be simplified to:

struct node
{
   int data;
   node * next;
};

Links:

Are C++ recursive type definitions possible, in particular can I put a vector<T> within the definition of T?
Difference between 'struct' and 'typedef struct' in C++?

edited May 23 '17 at 12:09

Community

1
1

answered Feb 25 '17 at 03:33

Janarth K

152
6

The disadvantage of the `struct node` shown is that you don't get the mapping facilities added automatically. – Jonathan Leffler Feb 25 '17 at 03:54
Hmm what about `struct node { map ptr;}` – Janarth K Feb 25 '17 at 04:43

Self-referential typedef without object or struct

1 Answers1