Here's a MWE:
#include <stdlib.h>
typedef struct node_type {
struct node* next;
struct node* prev;
} node;
int main(int argc, char* argv[]) {
node* n = (node*)malloc(sizeof(node));
}
Not having struct before node* in the struct definition will error; node has not yet been defined. However, struct node* works fine, even though only struct node_type has been defined at this point. Why does this work?
Intuitively, it compiles if the struct is defined with struct node_type* for its fields, or if there is an explicit typedef before and the fields are of type node*. However, I don't understand why an in-line typedef allows the fields to be of type struct node* but not of type node*.
Not having struct before node* in the struct definition will error; node has not yet been defined. However, struct node* works fine, even though only struct node_type has been defined at this point.
In this typedef declaration
typedef struct node_type {
struct node* next;
struct node* prev;
} node;
there are declared two structure types. The first one, struct node_type, is a complete type, and the second one, struct node, is an incomplete type.
Apart from these declarations, the code introduces an alias node for the type specifier struct node_type.
You may write
node* n = (node*)malloc(sizeof(node));
but you may not write for example
n->next = ( node * )malloc( sizeof( node ) );
or
n->next = malloc( sizeof( struct node ) );
because the type struct node is an incomplete type. Its size is unknown. And struct node * and node * are incompatible pointer types.
As for your question then if you will write for example
typedef struct node_type {
node* next;
node* prev;
} node;
then in these member declarations
node* next;
node* prev;
the name node is not defined yet. So, the compiler issues an error message.