How to implement and share an inlined function using C99?

Question

With gnu89:

/* share.h */
extern inline void f (void);
/* function.c */
void f (void) {}
/* main.c */
#include "share.h"
int main (int argc, char **argv) {
    f ();
    return 0;
}

With C99:

/* share.h */
static inline void f (void) {}
/* main.c */
#include "share.h"
int main (int argc, char **argv) {
    f ();
    return 0;
}

How to implement one definition of f() in function.c like in gnu89 but using C99 mode?

Answer 1

You put the inline definition the header file without extern and add an extern declaration/prototype in a source file:

/* share.h */
inline void f(void) {}

/* function.c */
#include "share.h"
extern void f(void);

/* main.c */
#include "share.h"
int main(int argc, char *argv[])
{
    f();
    return 0;
}

See http://www.greenend.org.uk/rjk/2003/03/inline.html for more information about inline in C.

If you really want to keep all your definitions (inline or not) in function.c like you say:

/* share.h */
#define WANT_INLINE 1
#include "function.c"

/* function.c */
#ifdef WANT_INLINE
inline void f(void) {}
#else
#include "share.h"
extern void f(void);
#endif

Not heavily tested and not recommended.