union inside structure

where union inside structure is used....

as i know structure inside union is used when we need to access the variable of abstract type and also its lower part ...
ex.., individual bit of integer and whole integer can be accessed with this.

but where union inside structure is used... this is interview question
(i'm an embedded software professional... expecting an answer in embedded point of view)

This is what I found in my book.
Suppose we wish to store information about employees in an organization.

Quote:

---

Name Grade Age
If grade=HSK(Highly skilled)
hobby name
credit card number
If Grade=SSK(Semi skilled)
Vehicle no.
Distance from Company

---

We can use a single structure for it but then it would lead to wastage of memory coz either hobby name & credit card no. or vehicle no. & distance from com. is used at a time. Both of them are never used simultaneously. So, here union inside structure can be used effectively:

Code:

---

struct info1
{
char hobby[10];
int crcardno;
};
struct info2
{
char vehno[10];
int dist;
};
union info
{
struct info1 a;
struct info2 b;
};
struct emp
{
char n[20];
char grade[4];
int age;
union info f;
};
struct emp e;

---