extern and struct size question

[stianlex]

I received, among others, the following two questions at some tests here at my university, but I’m not sure about the right answers. The questions are for the C language, not C++.

Q1 Assuming that addresses are represented on 4 bytes, how much memory space is reserved by the following declarations:

extern long count;
struct node {
    long key;
    struct node *next;
};

A 0 bytes; B 4 bytes; C 8 bytes; D 12 bytes;

Q2 Assuming that addresses are represented on 4 bytes, how much memory space is reserved by the following declarations:

extern long count;
struct node {
    long key;
    struct node *next;
} val;

A 0 bytes; B 4 bytes; C 8 bytes; D 12 bytes;

Which are the right answers and why?
Thanks in advance!

[Duthomhas]

Remember that extern just tells the compiler that something already exists elsewhere.

Also remember that a type declaration doesn't actually reserve any memory -- all it does is tell the compiler how to organize (or view) some piece of memory.

The only time memory is reserved is when actually declaring variables.

Hope this helps.

[stianlex]

Let's see...

For Q1, extern takes 0 bytes and struct also 0 bytes, so right answer A 0 bytes.

For Q2, extern takes 0 bytes, but struct, being declared there as val, takes 4 bytes for the long variable and 4 bytes for the pointer to struct variable, so right answer C 8 bytes.

If I answered correctly that means that I got it. :D

Thanks once again!
And last but not least, I liked the way you managed to reply, you didn't provided me directly the answers, but guided me and let me think about which ones are correct.