bar.c

#include "bar.h"

#include <stdlib.h>

void bar_init(struct bar* self,
              int member1)
{
    self->member1 = member1;
    self->member2 = "Hello, World!";
    self->member3 = NULL;
}

int bar_getmember1(struct bar* self)
{
    return self->member1;
}

bar.h

struct bar {
    int member1;
    
    union { const char* member2; };
    
    void (*member3)(unsigned short*);
    
    union why {
        struct {
            int madness[10];
            struct {
                int totally[6];
                void* thing;
            };
        };
        
        const char* something;
    };

};

void bar_init(struct bar*,
              int member1);

int bar_getmember1(struct bar*);

example.c

#include "bar.h"

#include <stdio.h>

void main(void)
{
    struct bar my_bar;
    
    bar_init(&my_bar, 123);
    
    printf("my_bar->member1 = %d \n", bar_getmember1(&my_bar));
}