prototypes for 'static' functions

Question

I'm not quite sure if it is really necessary to have prototypes for static functions in C. As long as I'm not exporting such functions (i.e. they don't have external linkage), what other benefit can this give?

Thanks.

Answer 1

To cite some authority, MISRA-C:2004 rule 8.1 enforces prototypes for functions with external linkage, but also mentions internal linkage:

"The provision of a prototype for a function with internal linkage is good programming practice."

I take it this is good practice because it makes your coding style between interal/external linkage functions consistent. And as others have mentioned in their answers, it is convenient as well.

Answer 2

E.g. if you need to ensure that a function has a certain type, it can be useful.

Consider this:

// Define how the functions should be defined.
typedef void * jobfunc(void *);

// Use case
void addjob(jobfunc *);

// Ensure they have the right type. Without this, you only get a warning
// for addjob(job2) (see below) - with it, you get an error for the mismatch.
static jobfunc job1;
static jobfunc job2;

// Define one job
static void * job1(void * arg) {
    return NULL;
}

// Define another job - accidentally wrong.
static void * job2(int accidentally_wrong) {
    return NULL;
}