Question

I made a template list with help of macroses. And I have an error, when I use it in more then one time in the code. There is a link error LNC2005 in MS VS.
I think, it happens, because bodies of functions are in the header, is there another way to keep them?

#define  GENERIC_LIST_POSTFIX  i
#define  GENERIC_LIST_TYPE     int
#define  GENERIC_LIST_NAME     list

#include "generic_list.h"

#undef  GENERIC_LIST_POSTFIX
#undef  GENERIC_LIST_TYPE   
#undef  GENERIC_LIST_NAME  

If I can’t change a language, what can You advice to me?
Thanks.

There is my code

#ifndef _GENERIC_LIST_H
#define _GENERIC_LIST_H

#define _CAT(x,y)    x##y
#define  CAT(x,y)  _CAT(x,y)

#if !defined GENERIC_LIST_POSTFIX 
#   error("GENERIC_LIST_POSTFIX")
#endif

#if !defined GENERIC_LIST_TYPE
#   error("GENERIC_LIST_TYPE")
#endif
#if !defined GENERIC_LIST_NAME 
#   error("GENERIC_LIST_NAME")
#endif
//-------------------------------------------------------------------------------
typedef struct CAT(CAT(_list_,GENERIC_LIST_POSTFIX),_node) CAT(GENERIC_LIST_NAME,_node);
struct CAT(CAT(_list_,GENERIC_LIST_POSTFIX),_node)
{ GENERIC_LIST_TYPE value;
  struct CAT(CAT(_list_,GENERIC_LIST_POSTFIX),_node) *prev;
  struct CAT(CAT(_list_,GENERIC_LIST_POSTFIX),_node) *next;
};

//typedef struct CAT(_list_,GENERIC_LIST_POSTFIX) GENERIC_LIST_NAME;
struct CAT(_list_,GENERIC_LIST_POSTFIX)
{ unsigned int len; // number of elements
  struct CAT(CAT(_list_,GENERIC_LIST_POSTFIX),_node) *first;
  struct CAT(CAT(_list_,GENERIC_LIST_POSTFIX),_node) *last;
};
//-------------------------------------------------------------------------------
void   CAT(CAT(list_,GENERIC_LIST_POSTFIX),_create )
(struct CAT(_list_,GENERIC_LIST_POSTFIX) *List);
{ List->len   = 0; List->first = NULL; List->last  = NULL; }

void   CAT(CAT(list_,GENERIC_LIST_POSTFIX),_copy   )
(struct CAT(_list_,GENERIC_LIST_POSTFIX) *scr, struct CAT(_list_,GENERIC_LIST_POSTFIX) *dest);
{ // ... }
// ... there are more code
#endif

All works, but there is another problem.
I can use this .h file only one time in a one .c file.
If I define GENERIC_LIST_TYPE firstly as int, than as int*, for example.

#define  GENERIC_LIST_POSTFIX  i
#define  GENERIC_LIST_TYPE     int
#define  GENERIC_LIST_NAME     list_i

#include "generic_list.h"

#undef   GENERIC_LIST_POSTFIX
#undef   GENERIC_LIST_TYPE   
#undef   GENERIC_LIST_NAME  


#define  GENERIC_LIST_POSTFIX  pi
#define  GENERIC_LIST_TYPE     int*
#define  GENERIC_LIST_NAME     list_pi

#include "generic_list.h"

#undef   GENERIC_LIST_POSTFIX
#undef   GENERIC_LIST_TYPE   
#undef   GENERIC_LIST_NAME 

I don’t get 2 lists with list_i and list_pi names.
The second “list_pi” is “undeclared identifier”.
Is there a solution for this?
Thank you twice.

Answer 1

If I read your question right, you have a header like this:

void doSomething()
{
    printf("doing something");
}

Which causes link errors when you include the file multiple times.
However, if you make the function static:

static void doSomething()
{
    printf("doing something");
}

The method will not be put to the linker, so you won’t have to worry about linker errors.

Your other option is to put a method declaration in your header, and an implementation in a .c file elsewhere in your project.