C - Unknown type name - c

I need to build a "social network" for college, but I always get unknown type name 'List' while compiling. I removed a lot of functions from my headers, but I still get the same error and I don't know why.
I've got 3 headers:
My friend's header
#ifndef FRIEND_H
#define FRIEND_H
#include "ListHeadTail.h"
typedef struct Friend{
int id;
struct Friend *nextFriend;
}Friend;
void printFriends(List *l);
void removeFriend(List *l);
void addFriend(List *l);
#endif /* FRIEND_H */
My list header:
#ifndef LISTHEADTAIL_H
#define LISTHEADTAIL_H
#include "Student.h"
typedef struct pStudent{
struct pStudent *ant;
Student *s;
struct pStudent *prox;
}pStudent;
typedef struct list{
pStudent *head;
pStudent *tail;
}List;
void startList(List *l);
void printList(List *l);
void freeList(List *l);
#endif /* LISTHEADTAIL_H */
My student's header
#ifndef STUDENT_H
#define STUDENT_H
#define MAX 51
#include "Friend.h"
#include "ListHeadTail.h"
typedef struct Student{
int id;
char name[MAX];
Friend *friends;
}Student;
Student* readStudent ();
void printStudent(Student* a);
void changeData(List *l);
#endif /* STUDENT_H */
My main:
#include <stdio.h>
#include <stdlib.h>
#include "ListHeadTail.h"
#include "Friend.h"
#include "Student.h"
int main(int argc, char** argv) {
List l;
startList(&l);
freeList(&l);
return (EXIT_SUCCESS);
}
Thanks for reading.

Here's the (first) error I get when I try to compile this set of files:
$ cc main.c
In file included from main.c:4:
In file included from ./ListHeadTail.h:4:
In file included from ./Student.h:6:
./Friend.h:11:19: error: unknown type name 'List'
void printFriends(List *l);
Look at the file names and line numbers. Note that at ListHeadTail.h line 4, you've already defined LISTHEADTAIL_H, but you haven't yet reached the actual declaration of List. You then go into Student.h, and from there into Friend.h. That includes ListHeadTail.h again -- but since LISTHEADTAIL_H is already defined, this include does nothing. So you continue through Friend.h with no declaration of List, and therefore get an error on the declarations that reference it.
As noted by #lurker in their comment, the basic issue here is circular dependency, and a simple fix is forward declaration. In this case, you could simply modify Friend.H, replacing #include "ListHeadTail.h" with typedef struct list List;.
But to me this is a bit hacky. If you shift the order of includes somewhere, the build might break again.
I think the real problem is that the declarations of the functions (printFriends, etc.) don't belong in Friend.h; they belong in ListHeadTail.h. The functions have nothing to do with the Friend type. Sure, they have "Friend" in their names, but the only type referenced in the declarations is List. So they belong in ListHeadTail.h. Same goes for the changeData function in Student.h.
In an object-oriented design (say, in Java), these functions would all probably be methods of the List class, and would be declared in that class's source file.

Related

Unknown type name in C header file

I'm facing an issue when I compile my project. I'm trying to put in a queue a struct which I've decalred in a header file like this:
Appointment functions header file ("signupFunctions.h" is where I've my "Patient" declaration):
#ifndef appointmentFunctions_H__
#define appointmentFunctions_H__
#include "queueFunctions.h"
#include "signupFunctions.h"
typedef struct{
int cough;
int rDistress;
int fatigue;
int fever;
}symptoms;
typedef symptoms *Symptoms;
typedef struct {
Patient patient;
Symptoms symptoms;
int day;
int mon;
int year;
int flag;
}appointment;
typedef appointment *Appointment;
int getSymptomsValue(Appointment A);
void setSymptoms(Appointment A);
void requestAppointment(Patient P, qNodePtr *head, qNodePtr *tail);
#endif
Queue functions header file:
#ifndef queueFunctions_H__
#define queueFunctions_H__
#include "appointmentFunctions.h"
typedef struct qNode{
Appointment A;
struct qNode *next;
}QueueNode;
typedef QueueNode *qNodePtr;
void printQueue(qNodePtr currentPtr);
int isEmpty(qNodePtr head);
void dequeue(qNodePtr *head, qNodePtr *tail);
void enqueue(qNodePtr *head, qNodePtr *tail, Appointment App);
#endif
Once I compile I get:
In file included from appointmentFunctions.h:4:0,
from menuFunctions.h:5,
from main.c:4:
queueFunctions.h:7:2: error: unknown type name 'Appointment'
Appointment A;
^~~~~~~~~~~
queueFunctions.h:16:46: error: unknown type name 'Appointment'
void enqueue(qNodePtr *head, qNodePtr *tail, Appointment App);
^~~~~~~~~~~
In file included from appointmentFunctions.h:4:0,
from menuFunctions.h:5,
from signupFunctions.c:5:
queueFunctions.h:7:2: error: unknown type name 'Appointment'
Appointment A;
^~~~~~~~~~~
queueFunctions.h:16:46: error: unknown type name 'Appointment'
void enqueue(qNodePtr *head, qNodePtr *tail, Appointment App);
^~~~~~~~~~~
..and so on. What's the problem? Thanks in advance.
In appointmentFunctions.h you include queueFunctions.h
So when queueFunctions.h is read the type Appointment is unknown.
It doesn't help you that queueFunctions.h also includes appointmentFunctions.h because at that time appointmentFunctions_H__ is already defined, i.e. the file content will not be read.
If file X.h depends on something from file Y.h and at the same time Y.h depends on something from file X.h you have a design error that must be fixed.
As far as I can see the dependency is only pointer to struct so you can get rid of the dependency by forward declaring the struct.
In queueFunctions.h do these changes:
#include "appointmentFunctions.h" --> struct appointment;
Appointment --> struct appointment*
BTW: It's opinion based but most programmers avoid typedef's for pointers. If it's done it's typically a good idea to use a name that clearly tells that this is a pointer, i.e. something like:
typedef appointment *Appointment; --> typedef appointment *appointmentPtr;
You recursively included one header in another
#ifndef appointmentFunctions_H__
#define appointmentFunctions_H__
#include "queueFunctions.h"
#include "signupFunctions.h"
//...
and
#ifndef queueFunctions_H__
#define queueFunctions_H__
#include "appointmentFunctions.h"
//...
So the compiler issues an error.
You shall not do that.
That is the header appointmentFunctions.h at once includes the header queueFunctions.h in which there is declaration
typedef struct qNode{
Appointment A;
struct qNode *next;
}QueueNode;
but the declaration of Appointment is not visible yet. It follows after the inclusion of the header queueFunctions.h.

Use typedef from one header in another and vice versa

Suppose I have such a project structure:
main.c
#include "hashtable.h"
#include "list.h"
int main()
{
hash_table ht = calloc(1, sizeof(htable));
cmp_function f;
TLDI list;
return 0;
}
hashtable.h
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifndef _HASH_TABLE_
#define _HASH_TABLE_
#include "list.h"
typedef int (*hash_function)(void*, int);
typedef struct _hasht_{
int maxElemNumber;
hash_function hf;
TLDI* key_array;
} htable, *hash_table;
void test2(cmp_function cmp);
#endif
list.h
#include "hashtable.h"
#ifndef _LINKED_LIST_
#define _LINKED_LIST_
typedef int (*cmp_function)(void*, void*);
typedef struct _node_ {
void *info;
struct _node_ *pre, *urm;
} TNode, *TLDI;
int test(hash_table ht);
#endif
and another two C files:
hash_func.c
#include "hashtable.h"
void test2(cmp_function cmp)
{
printf("test\n");
}
list_func.c
#include "list.h"
int test(hash_table ht)
{
return 1;
}
I want to use in hashtable.h a typedef from list.h, it's typedef struct...},*TLDI;. In the same way, list.h uses a typedef struct ...},*hash_table; from hashtable.h. Can I do something like this or I'm wrong? Cause I get this error while compiling whole project:
In file included from hashtable.h:7,
from main.c:1:
list.h:14:10: error: unknown type name ‘hash_table’
14 | int test(hash_table ht);
In file included from hashtable.h:7,
from hash_func.c:1:
list.h:14:10: error: unknown type name ‘hash_table’
14 | int test(hash_table ht);
I'm not strong in typedef and headers, but if I would get an answer to this question or at least a source from where I could find out more about them I would be very grateful.
Two headers that rely to each other are not a show stopper if well-formed. What I observe is that your include guards don't enclose the full header but only part of it, this I think is wrong. The right way to use include guards is shown in this
example header some_component.h:
#ifndef SOME_COMPONENT_H
#define SOME_COMPONENT_H
// include whatever you need here (*after* the opening guard):
#include "some_other_component.h"
// start type definitions and declarations *after* includes:
struct some_component_t {
// ...
};
#endif
This way, you headers will work most consistently:
either read completely
or completely ignored
I advise you to avoid placing definitions before includes, as this allows you to modify the content of the included content. What looks like a tempting idea at first, turns into a confusing nightmare in the long run in the vast majority of cases.
Another point is that if the definitions in the two headers really rely on each other, you should rethink your design.
Also, it's not clear why void test2(cmp_function cmp); which relies on cmp_function is declared in hashtable.h and why int test(hash_table ht); which relies on hash_table is declared in list.h; to me this seems like you were mixing up things here. In other words, by switching places of some declarations, you'd get rid of most of the entanglement.
You should also know that typedefs and pointers are allowed on incomplete types, so it's possible to declare a pointer to a structure that is not yet defined. So, for example, the following compiles:
typedef int (*hash_function)(void*,int);
typedef int (*cmp_function)(void*,void*);
typedef struct _hasht_ hasht, *hash_table;
typedef struct _node_ TNode, *TLDI;
struct _node_ {
void *info;
struct _node_ *pre, *urm;
};
struct _hasht_{
int maxElemNumber;
hash_function hf;
TLDI* key_array;
};
... as does this (version without struct typedefs):
struct _node_ {
void *info;
struct _node_ *pre, *urm;
};
typedef int (*hash_function)(void*,int);
struct _hasht_{
int maxElemNumber;
hash_function hf;
struct _node_** key_array;
};
The overall interdependency of the headers is kind of ugly, but the errors can be corrected with some forward declarations:
hashtable.h
#ifndef _HASH_TABLE_
#define _HASH_TABLE_
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct _hasht_ htable, *hash_table;
typedef int (*hash_function)(void*,int);
#include "list.h"
struct _hasht_ {
int maxElemNumber;
hash_function hf;
TLDI* key_array;
};
void test2(cmp_function cmp);
#endif
list.h
#ifndef _LINKED_LIST_
#define _LINKED_LIST_
typedef struct _node_ TNode, *TLDI;
typedef int (*cmp_function)(void*,void*);
#include "hashtable.h"
struct _node_ {
void *info;
struct _node_ *pre, *urm;
};
int test(hash_table ht);
#endif

"unknown type name" in c struct while ussing gcc

I have a program which is processing list in c, it is working perfectly as long as I have it in one source file, when I try to separate it and compile it got this error “ delete_functions.c:15:13: error: unknown type name ‘nodetype’ ” same error goes for functionality_functions.c and insert_functions.c here is the code
main.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "types.h"
#include "delete_functions.h"
#include "insert_functions.h"
#include "functionality_functions.h"
int main(){
//i did not upload all the main function code because it is way to long
}
types.h
typedef char AirportCode[4];
typedef struct nodetype{
char Airport[4];
struct nodetype *next;
} nodetype;
delete_functions.h
void Delete(nodetype *list,char node[4]);
void DeleteLast(nodetype *list);
functionality_functions.h
void print(nodetype *head);
nodetype *search(nodetype *list,char item[4]);
nodetype *create();
insert_functions.h
void *InsertLast(nodetype *list,char item[4]);
void *InsertAfter(nodetype *list,char item[4],char node[4]);
According to the GCC error message, there error is in the delete_functions.c file.
Presumably, it looks like this at the beginning:
#include "delete_functions.h"
Since delete_functions.h does not itself include types.h, you need to include it first:
#include "types.h"
#include "delete_functions.h"
Alternatively, you can add include guards to your headers so, that they can safely be included multiple times, like this for types.h:
#ifndef TYPES_H
#define TYPES_H
typedef char AirportCode[4];
typedef struct nodetype{
char Airport[4];
struct nodetype *next;
} nodetype;
#endif
And for delete_functions.h:
#ifndef DELETE_FUNCTIONS_H
#define DELETE_FUNCTIONS_H
void Delete(nodetype *list,char node[4]);
void DeleteLast(nodetype *list);
#endif
The *_H include guard macros are necessary because otherwise, main.c would not compile anymore: each type in types.h can only be defined once per translation unit, and without the guards, every *.h would bring in another definition, leading to compiler errors.

"already defined " error in VC++

I am learning to write programs in professional way. Like, by creating separate .C and .h file.i decided to write a simple code with structures but I am getting errors.
I have done these things :
/*---list.h file-------*/
#ifndef LIST_H
#define LIST_H
struct list{
int a;
struct list *next;
};
typedef struct list LIST;
LIST *pHead=NULL,*pCurrent=NULL;
void display(void);
#endif
/*---list.c file ---*/
#include "main.h"
void display()
{
pHead->a=100;
printf("%d",pHead->a);
}
/*----main.h file-----*/
#ifndef MAIN_H
#define MAIN_H
#include<stdio.h>
#include "list.h"
#endif
/*---main.c file---*/
#include "main.h"
void main(void)
{
LIST *New=pHead;
display();
printf("\n\n%d",New->a);
getch();
}
when i compile the code , I am getting following errors
1>main.obj : error LNK2005: _pCurrent already defined in list.obj
1>main.obj : error LNK2005: _pHead already defined in list.obj
can anyone please tell me what I am doing wrong ? Am I including something twice because of which I am getting redeclaration error ?
This is because you define things in your header, as opposed to merely declaring them.
This:
LIST *pHead=NULL,*pCurrent=NULL;
means that every C file that includes the list header, tries to create two global variables. When you then link these C files together, those variables collide. This is broken, you should never do that. Never define things in a header.
You defined the objects in a header file and then included them in multiple source files thus breaking the one definition rule.
If you want to create global variables which you can use across different translation units, you should use the extern keyword.
Generally speaking, .c files contain embodiment of variables, functions, etc.; while .h files contain prototypes of variables, functions, etc., found in it's companion .c file.
It is generally the case that variable and function bodies are not placed in a .h file; only variable and function prototypes should be placed in .h files.
When considering how to split-up code into separate files, it is important to consider which functions, structures and macros are the most primitive. For example, if you write two functions, and function 'a' calls function 'b', function 'b' is most primitive.
The idea is to group functions into a 'c' file that are related, and are at a similar primitive level.
In the case of this question, the more primitive list functions should be embodied in list.c. Then 'list.h' is used to prototype functions and structures used by other less primitive .c files such as main.c.
The most primitive functions are also the most self sufficient. While less primitive functions should call more primitive functions, the reverse makes for clumsy code-flow.
Now to review the question code:
/*---list.c file ---*/
#include "main.h"
list.c should be considered as more primitive than main.c. Hence, having list.c include main.h is (professionally) not a good idea. list.c, being more primitive should be more self-sufficient.
Rather than including main.h, it would be better for list.c to include it's own list.h so that it has access to it's own `struct list' definition, etc.
void display()
{
pHead->a=100;
printf("%d",pHead->a);
}
In order to better isolate list.c, the above function should not reference a 'global' variable (pHead). Rather, it would be better to have the 'node to display' passed into the function as an argument.
With this in mind, here are how 'list.c' and 'list.h' might be improved:
/*---list.h file-------*/
#ifndef LIST_H
#define LIST_H
typedef struct NODE_S
{
int a;
struct list *next;
} NODE_T;
typedef struct LIST_S
{
NODE_T *head;
} LIST_T;
extern void NodeDisplay(NODE_T *node);
#endif
/*---list.c file ---*/
#include <stdio.h> // printf()
#include "list.h" // NODE_T, LIST_T
void NodeDisplay(NODE_T *node)
{
printf("%d\n",pHead->a);
return;
}
Note that pHead and pCurrent are not prototyped, or embodied, in list.h or list.c Those variables are not used in list.c, and there is no functional reason to place them in list.h
Now examine main.h and main.c as they are in the question code:
/*----main.h file-----*/
#ifndef MAIN_H
#define MAIN_H
#include<stdio.h>
#include "list.h"
#endif
In isolation, what is the purpose that main.h requires stdio.h and list.h? If they were removed, would there be something left 'undefined' in 'main.h'? Perhaps these two include files don't really belong in main.h. "But if they are removed from main.h, why even have a main.h?" Good point. perhaps main.h serves no purpose and perhaps should not even exist.
The main.c file is the least primitive of all files, and shouldn't generally export anything to other (more primitive) files.
/*---main.c file---*/
#include "main.h"
void main(void)
{
LIST *New=pHead;
display();
printf("\n\n%d",New->a);
getch();
}
So what exactly does main.c need? It needs calls printf(), so it will need to include stdio.h. It calls display(), and references the LIST structure, so it needs list.h.
Yes, those .h files were included in main.h; good point. However, the code will be less clumsy (more professional) if main.c includes exactly what it needs explicitly.
With this philosophy in mind, here is a reworked main.c, without a superfluous main.h:
/*---main.c file---*/
#include <stdio.h> // printf()
#include <conio.h> // getch()
#include "list.h" // NodeDisplay(), LIST_T
int main(void)
{
LIST_T pList =
{
.head = NULL
};
/* Allocate & Insert a node into the list. */
NodeCreate(&pList, 100);
NodeDisplay(pList.head);
getch();
return(0);
}
This version of main.c includes exactly what is required, and appropriately calls less primitive functions. It has no need for 'global variables' because it passes its local storage to more primitive functions as needed.
Oh! you noticed the function NodeCreate()!
While the operation of allocating and inserting a new list node could be performed in main.c, such an operation is most likely a common occurrence that fits nicely with other linked list operations. Hence, add such a function to list.c:
/*---list.c file ---*/
#include <stdio.h> // printf()
#include <stdlib.h> // malloc()
#include "list.h" // NODE_T, LIST_T
void NodeDisplay(NODE_T *node)
{
printf("%d\n",node->a);
return;
}
void NodeCreate(LIST_T *list, int a)
{
NODE_T *newNode = malloc(sizeof(*newNode));
if(NULL == newNode)
{
fprintf(stderr, "malloc(newNode) failed.\n");
goto CLEANUP;
}
if(NULL == list)
{
fprintf(stderr, "Passing NULL as the list address not allowed.\n");
goto CLEANUP;
}
/* Initialize new node fields (payload) */
newNode->a = a;
/* Link newNode as new 'list head' node. */
newNode->next = list->head ? list->head->next : NULL;
list->head = newNode;
newNode=NULL;
CLEANUP:
if(newNode)
free(newNode);
return;
}
And so that this function can be called from the less primitive main.c, add a prototype of the function to list.h:
/*---list.h file-------*/
#ifndef LIST_H
#define LIST_H
typedef struct NODE_S
{
int a;
struct list *next;
} NODE_T;
typedef struct LIST_S
{
NODE_T *head;
};
extern void NodeDisplay(NODE_T *node);
extern void NodeCreate(LIST_T *list, int a);
#endif
See spoiler code here.

Declaring the various typedefs in a stack ADT

Here's my problem: I need to implement a FIFO/LIFO list stack as ADT species 1. My program is modular and it have an item.h module:
#ifndef ITEM_H_INCLUDED
#define ITEM_H_INCLUDED
typedef struct
{
char stringa[20];
int numero;
} Item;
#endif // ITEM_H_INCLUDED
The head.h module:
#ifndef HEAD_H_INCLUDED
#define HEAD_H_INCLUDED
#include <stdio.h>
#include <stdlib.h>
#include "item.h"
void QUEUEinit();
int QUEUEempty();
void QUEUEput_top(Item);
void QUEUEput_bottom(Item);
Item QUEUEget_top();
Item QUEUEget_bottom();
#endif // HEAD_H_INCLUDED
The main.c and data.c; what i need is how i declare a QEUEnode struct and where.
Thank you for the help :)
Since none of your QUEUE* functions receive a QUEUEnode *, you can hide it in the head.c file, along with the QUEUEnode root; that they operate on.
If you want to use multiple queues, then it should probably be in the head.h file so they can be created in main.c. For this, you'll also need to modify the functions to accept a queue to operate on.

Resources