forward declaration not working , does not have a type error

问题

I use forward declaration but still get ERROR: 'link' does not name a type. Why?

struct link;

struct node
{
    link *head_link;            <------- this is the error location
    node *next_node;
};

struct link
{
    link *next_link;
    node *connect_node;
};

回答1:

You declare a type called struct link, it's not just link, so write:

struct node
{
    struct link *head_link;
    struct node *next_node;
};

Alternatively, declare a type called link with a typedef.

来源：https://stackoverflow.com/questions/18009716/forward-declaration-not-working-does-not-have-a-type-error