Calling function pointed by void* pointer

Question

I have an event struct that looks like this

typedef struct {
    void* fn;
    void* param;
} event;

How can I call this function by pointer as part of the struct. For example, these do not work:

event->(*function)();
event->function();
(*event->function)();

I want to know how to make the function call both with and without using the additional void* param. I was originally using this link as a reference:

http://www.cprogramming.com/tutorial/function-pointers.html

I've used these function pointers before, but have trouble getting the syntax correct.

Answer 1

You need to cast void* pointer to the function pointer first:

#include <stdio.h>

typedef struct {
    void* fn;
    void* param;
} event;

void print()
{
        printf("Hello\n");
}


int main()
{
    event e;
        e.fn = print;
        ((void(*)())e.fn)();
        return 0;
}

Of course, if this is really what you want. If you want your struct to contain pointer to the function, instead of void* pointer, use the proper type at the declaration:

typedef struct {
    void (*fn)();
    void* param;
} event;

Here you have fn declared as a pointer to the void function, and the param as void* pointer.

Answer 2

If I understood correctly, you're probably looking for this:

typedef struct {
    void (*fn)();
    void (*param)();
} event;


event *E;

E->fn();
E->param();