void (*foo)(void) : meaning of latest (void)

Question

B.A.T.M.A.N./A.L.F.R.E.D. OpenMesh project:

function read_answer instantiates a pointer to a type struct vis_print_ops that is defined

struct vis_print_ops
{
    void (*preamble)(void);
    void (*interfaces)(uint8_t iface_n, struct vis_iface *ifaces);
    void (*entries)(uint8_t entries_n, struct vis_entry *vis_entries,
            uint8_t iface_n, struct vis_iface *ifaces);
    void (*postamble)(void);
};

Now look at

void (*preamble)(void)

could you please tell me what is the meaning of the last (void)? Isn't

void (*preamble)

enough?

It essentialy means it's a function pointer with no parameters. — Linus, Oct 19 '15 at 14:41

score 5 · Answer 1 · answered Oct 19 '15 at 14:43

5

The last void means that there are no arguments in function that will be pointed by preamble.

void (*preamble) isn't enough because this is only a pointer to void whereas void (*preamble)(void) is a function pointer.

answered Oct 19 '15 at 14:43

MikeCAT

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1

Would `void (*preamble)()` be okay? – Germano Massullo Oct 19 '15 at 14:44
3

@Caterpillar, no, that is not the same. It means that `preamble` takes some undefined arguments. – Kijewski Oct 19 '15 at 14:45

Linus · Answer 2 · 2015-10-19T14:47:58.277

5

It means that your declaring a function pointer with no parameters. It's not more complicated than that. It is similiar to something like: int main(void) and int main()

Both are the same. Be careful though as discussed in the comments, if you declare a function pointer without the void keyword and only the empty brackets it specifies a function pointer with undefined arguments.

edited Oct 19 '15 at 14:47

answered Oct 19 '15 at 14:43

Linus

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@cad Correct, I edited my answer. Thanks! – Linus Oct 19 '15 at 14:48

void (*foo)(void) : meaning of latest (void)

2 Answers2