Re: 'Base class' shared libraries in C?

[Max Okumoto <okumoto@xxxxxxxx>]

Jonathon McKitrick wrote:
> Hi all,
>
> I am trying to implement some C++ functionality in C.
>
> Suppose I have several libraries that share behavior and properties, such as
> version, working directory, and so on.  I want other libraries to extend
> this behavior without having to duplicate any code.  For instance:
>
> typedef struct base
> {
> 	char version[32];
> 	char path[32];
> } base_t;

I would not use *_t as the name of the typedef.  It might
conflict with a standard C or POSIX defintion in the future.
Just use base, since that allows you to hide the definition.
It will reduce your compile times when you modify a header file.

/* base.h */
typedef struct base {
	int	num;
	/* stuff */
} base;


/* app.h */
struct base;		/*
			 * base.h does not need to be included
			 * in app.h since only references are
			 * passed.
			 */

struct AppStuff {
	struct base	*info;
};

void foo(struct base *);

/* app.c */
#include "base.h"	/*
			 * base.h is included because bar() uses
			 * the num field.
			 */

static void
bar(base *b)
{
	printf("%d\n", b->num);
}

void
foo(base *b)
{
	bar(b);
}


			Max Okumoto




> typedef struct foo
> {
> 	base_t *base;
> 	int data;
> } foo_t;
>
> typedef struct bar
> {
> 	base_t *base;
> 	int data;
> } bar_t;
>
> lib-base.so:
> 	base_get_version(base_t *, char *);
> 	base_get_path(base_t *, char *);
>
> lib-derived-foo.so:
> 	foo_one_method(foo_t *, int data);
> 	foo_two_method(foo_t *, int data);
>
> lib-derived-bar.so:
> 	bar_one_method(bar_t *, int data);
> 	bar_two_method(bar_t *, int data);
>
> I want the derived modules to link with the base library, so that my
> application can link with only the derived modules and still be able to call
> the base functions without having to link to that library or call 'wrapper'
> functions in the derived modules.
>
> Is there a way to do this?
>
> jm