What's the C strategy to "imitate" a C++ template ?
- by Andrei Ciobanu
After reading some examples on stackoverflow, and following some of the answers for my previous questions (1), I've eventually come with a "strategy" for this.
I've come to this:
1) Have a declare section in the .h file. Here I will define the data-structure, and the accesing interface. Eg.:
/**
* LIST DECLARATION. (DOUBLE LINKED LIST)
*/
#define NM_TEMPLATE_DECLARE_LIST(type) \
typedef struct nm_list_elem_##type##_s { \
type data; \
struct nm_list_elem_##type##_s *next; \
struct nm_list_elem_##type##_s *prev; \
} nm_list_elem_##type ; \
typedef struct nm_list_##type##_s { \
unsigned int size; \
nm_list_elem_##type *head; \
nm_list_elem_##type *tail; \
int (*cmp)(const type e1, const type e2); \
} nm_list_##type ; \
\
nm_list_##type *nm_list_new_##type##_(int (*cmp)(const type e1, \
const type e2)); \
\
(...other functions ...)
2) Wrap the functions in the interface inside MACROS:
/**
* LIST INTERFACE
*/
#define nm_list(type) \
nm_list_##type
#define nm_list_elem(type) \
nm_list_elem_##type
#define nm_list_new(type,cmp) \
nm_list_new_##type##_(cmp)
#define nm_list_delete(type, list, dst) \
nm_list_delete_##type##_(list, dst)
#define nm_list_ins_next(type,list, elem, data) \
nm_list_ins_next_##type##_(list, elem, data)
(...others...)
3) Implement the functions:
/**
* LIST FUNCTION DEFINITIONS
*/
#define NM_TEMPLATE_DEFINE_LIST(type) \
nm_list_##type *nm_list_new_##type##_(int (*cmp)(const type e1, \
const type e2)) \
{\
nm_list_##type *list = NULL; \
list = nm_alloc(sizeof(*list)); \
list->size = 0; \
list->head = NULL; \
list->tail = NULL; \
list->cmp = cmp; \
}\
void nm_list_delete_##type##_(nm_list_##type *list, \
void (*destructor)(nm_list_elem_##type elem)) \
{ \
type data; \
while(nm_list_size(list)){ \
data = nm_list_rem_##type(list, tail); \
if(destructor){ \
destructor(data); \
} \
} \
nm_free(list); \
} \
(...others...)
In order to use those constructs, I have to create two files (let's call them templates.c and templates.h) .
In templates.h I will have to NM_TEMPLATE_DECLARE_LIST(int), NM_TEMPLATE_DECLARE_LIST(double) , while in templates.c I will need to NM_TEMPLATE_DEFINE_LIST(int) , NM_TEMPLATE_DEFINE_LIST(double) , in order to have the code behind a list of ints, doubles and so on, generated.
By following this strategy I will have to keep all my "template" declarations in two files, and in the same time, I will need to include templates.h whenever I need the data structures. It's a very "centralized" solution.
Do you know other strategy in order to "imitate" (at some point) templates in C++ ? Do you know a way to improve this strategy, in order to keep things in more decentralized manner, so that I won't need the two files: templates.c and templates.h ?
