Data structures question

[Shwetabh]

Hi everyone.
My question is, why are data structures implemented only with struct
data type?
Why not union when it is more efficient as compared with structures?

Thanks in advance

[Eric]

Shwetabh <sh**********@g mail.com> wrote:

My question is, why are data structures implemented only with struct
data type?
Why not union when it is more efficient as compared with structures?

Well, depending on what I need to do, I will use which ever one is most
appropriate.

They are not interchangeable , but since you seem to be implying that
they are, I am wondering if you really understand the differences
between them.

[Emmanuel Delahaye]

Shwetabh wrote on 26/07/05 :

My question is, why are data structures implemented only with struct
data type?
Why not union when it is more efficient as compared with structures?

I don't see what you meant. Just implement the data structures in the
way that seems to be the best for your application. If you want an
union, 'just do it'...
--
Emmanuel
The C-FAQ: http://www.eskimo.com/~scs/C-faq/faq.html
The C-library: http://www.dinkumware.com/refxc.html

"It's specified. But anyone who writes code like that should be
transmogrified into earthworms and fed to ducks." -- Chris Dollin CLC

[John Bode]

Shwetabh wrote:

Hi everyone.
My question is, why are data structures implemented only with struct
data type?
Why not union when it is more efficient as compared with structures?

Thanks in advance

Unions are not more "efficient" than structs, any more than sizeof is
more efficient than strlen(); they are different entities, with
different purposes. You can't replace one with the other.

[Alex Fraser]

"John Bode" <jo*******@my-deja.com> wrote in message
news:11******** **************@ g14g2000cwa.goo glegroups.com.. .

Shwetabh wrote:

Hi everyone.
My question is, why are data structures implemented only with struct
data type?
Why not union when it is more efficient as compared with structures?

Thanks in advance

Unions are not more "efficient" than structs, any more than sizeof is
more efficient than strlen(); they are different entities, with
different purposes. You can't replace one with the other.

Consider:

struct foo {
enum foo_type t; /* specifies which member of u is valid */
union {
int i;
unsigned u;
/* ... */
} u;
};

In this case, with what I hope is obvious use, you can replace the union
with a struct (without affecting correctness), but doing so increases the
size of struct foo making it less memory efficient.

Alex

[Lawrence Kirby]

On Tue, 26 Jul 2005 12:18:45 -0700, Shwetabh wrote:

Hi everyone.
My question is, why are data structures implemented only with struct
data type?
Why not union when it is more efficient as compared with structures?

Thanks in advance

A union only allows you have have data stored in one of its members at any
particular time. When that is what you need you can use a union. However
most datastructures require data to be stored in more than one member at
ther same time so a union would not work and you would use a structure for
those.

Lawrence