c - "Error: unknown type name ..." while working on a 1st-class ADT fused with a 2nd-class ADT. -

good morning everybody.

i'm new here on so, , i'm asking question because have readjust algorithms , programming's exam of yesterday. while typing exam on codeblocks, got error couldn't fix. basically, exam asked load on memory infos file (format: char *namecity, int population, int distance) in data structure, , asked calculate mutual distances each city , collect them in data structure. decided make 2 adts: first defined in library "vett.h":

#ifndef vett_h_included #define vett_h_included #include "list.h"  typedef struct vett {     char nome[21];     int abitanti, dist;     lista_t list; } item;  item *vectinit(int n, item *v); item *vectinsert(item *v, char *nome, int people, int dist, int i); #endif // vett_h_included 

i made "almost-adt" or "2nd class adt" (r.sedgewick) based on teacher lessons. doing so, main create array struct, , have direct access fields of struct; each "cell" contains: name of city, population, distance, , list-type field. problem begins here. calculate , save mutual distances of cities, decided make adt list, type 1st class, in library called "list.h" :

#ifndef list_h_included #define list_h_included  #include "vett.h"  typedef struct lista *lista_t;  lista_t calculatemutualdistance(lista_t list, item *v, int n, int dist); int chechforbetter(int sd, int i, int n, item *v); lista_t listinit(lista_t list, int n);  #endif // list_h_included` 

the file "list.c" contains struct pointed in .h file:

#include <stdio.h> #include <stdlib.h> #include <string.h> #include "list.h"  typedef struct node *node; struct node {     char destination[21];     int distance;     node next; };  struct lista {     node head, tail; };  (...) 

now got error codeblocks (in vett.h, line 9, after int abitanti, int dist):

" error: unknown type name 'lista_t' ".

but why? lista_t contained in list.c file , should visible "vett.h", because included "list.h" , pointer finds struct in "list.c", has got "list.h" inclusion too!

hope can explain me, because have 2 days adjust program , make work, , it's quite huge. attention , sorry grammar errors, can tell i'm not english. have nice day!

it's typically forward declaration problem. change list.h file :

#ifndef list_h_included #define list_h_included  typedef struct vett item; typedef struct lista *lista_t;  lista_t calculatemutualdistance(lista_t list, item *v, int n, int dist); int chechforbetter(int sd, int i, int n, item *v); lista_t listinit(lista_t list, int n);  #endif // list_h_included`