Calling function pointed by void* pointer

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.