#include <stdio.h>
#include <string.h>
#include <stdlib.h>


enum types { INT, FLOAT, CHAR_20 };


struct field
{
    enum types type;
    union
    {
        int i;
        float f;
        char str[20];
    } data;
};


void print_field(struct field *f)
{
    switch (f->type)
    {
    case INT:
        printf("%d\n", f->data.i);
        break;
    case FLOAT:
        printf("%f\n", f->data.f);
        break;
    case CHAR_20:
        printf("%s\n", f->data.str);
        break;
    default:
        fprintf(stderr, "error: reached default case in switch, %s:%d\n",
                        __FILE__, __LINE__);
        abort();
    }
}


/* demo */
int main(void)
{
    struct field my_field;


    my_field.type = INT;
    my_field.data.i = 42;
    print_field(&my_field);


    my_field.type = FLOAT;
    my_field.data.f = 3.14159;
    print_field(&my_field);

    my_field.type = CHAR_20;
    strcpy(my_field.data.str, "hello, world!");
    print_field(&my_field);


    my_field.type = 42;
    print_field(&my_field); /* oops */


    return 0;
}