为什么结构不能成为其自身的成员？

Question

I have a struct foo . Declaring a member of type foo* works:

typedef struct foo
{
    struct foo* children[26];
} foo;

But if I try to declare a member of type foo I get an error:

typedef struct foo
{
    struct foo children[26];
} foo;

This declaration gives me the error

definition of 'struct foo' is not complete until the closing '}'

Answer 1

A structure T cannot contain itself. How would you know its size? It would be impossible to do so, because the size of T would require you to know the size of T (because T contains another T ). This turns into an infinite recursion.

You can have a pointer to T inside a structure T because the size of a pointer is not the same size as the pointed-to object: in this case, you would just store an address of memory where another T is stored - all the space you need to do that is basically the space you need to store a memory address where another T lives.

Answer 2

The structure Trie cannot contain another structure Trie in it , it will do a never - ending recursion but it may contain a pointer to another structure Trie

So first one is correct

typedef struct TRIE
{
    bool is_endpoint;
    bool is_initialized;
    struct TRIE* children[26];
} TRIE;

Answer 3

1. Object of type T can't contains another non-static object of same type. If it may be possible, how to find size of that object? Size of pointer to object is always constant on current system.
2. Check value of currentptr for non-NULL before you can access fields of currentptr (like is_endpoint ).