help w/ c/c++ problem

[Heinrich Pumpernickel]

28b (macros). write a macro, sizeof(var), that returns the size of
its argument . you are not allowed, to use the sizeof() operator for
this . for extra credit, write another macro, sizeof_t(type), that
returns the size of a type .

given is the following template....... ...

//////////////////////////////////////////////////////////////////////
// ASS28B.C
//////////////////////////////////////////////////////////////////////

#include <Stdio.H>

#define SIZEOF( var ) // FILL IN MACRO TEXT

void main()
{
char a;
short b;
int c;
long d;
long long e;
struct x* (*f)(struct y*);
union { int a[100]; float b[100]; } g;
void* h;

printf("sizeof a : %i\n", SIZEOF(a));
printf("sizeof b : %i\n", SIZEOF(b));
printf("sizeof c : %i\n", SIZEOF(c));
printf("sizeof d : %i\n", SIZEOF(d));
printf("sizeof e : %i\n", SIZEOF(e));
printf("sizeof f : %i\n", SIZEOF(f));
printf("sizeof g : %i\n", SIZEOF(g));
printf("sizeof h : %i\n", SIZEOF(h));
}

//////////////////////////////////////////////////////////////////////
can u hlp me w/ this ?

tnx !!!
--
mfg, heinrich :)

[Richard Heathfield]

Heinrich Pumpernickel said:

28b (macros). write a macro, sizeof(var), that returns the size of
its argument .

#define SIZEOF(x) (sizeof(x))

you are not allowed, to use the sizeof() operator for this .

Why not? That's what it's *for*.

given is the following template....... ...

<snip>

>
void main()

If your instructor gave you this template, you need a new instructor. In
C, main returns int.

<snip>

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Heinrich Pumpernickel]

On Jul 1, 5:04 am, Richard Heathfield <[e-mail].i nvalidwrote:

Heinrich Pumpernickel said:

28b (macros). write a macro, sizeof(var), that returns the size of
its argument .

#define SIZEOF(x) (sizeof(x))

but i m not allowed to do that

>

you are not allowed, to use the sizeof() operator for this .

Why not? That's what it's *for*.

well its just an excersise

>

given is the following template....... ...

<snip>

void main()

If your instructor gave you this template, you need a new instructor. In
C, main returns int.

i dont believe that . my c/c++ teacher (very experienced programmer)
AND the book were using both say that if main does not return a
value it can be declared void !

<snip>

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

--
mfg, heinrich :)

[Richard Heathfield]

Heinrich Pumpernickel said:

On Jul 1, 5:04 am, Richard Heathfield <[e-mail].i nvalidwrote:

>Heinrich Pumpernickel said:

28b (macros). write a macro, sizeof(var), that returns the size of
its argument .

#define SIZEOF(x) (sizeof(x))

but i m not allowed to do that

>>

you are not allowed, to use the sizeof() operator for this .

Why not? That's what it's *for*.

well its just an excersise

I hope that the point of the exercise is to demonstrate that there is no
satisfactory, portable solution to the problem, other than to change
the rules and allow use of the sizeof operator.

You can just about do it for objects:

#define SIZEOF(x) ((unsigned char *)(&(x)+1)-((unsigned char *)&(x))

but you can't do it for expressions or types without relying on
undefined behaviour, which is never wise if you can avoid it, and here
it can be avoided with ease by using sizeof.

given is the following template....... ...

<snip>

void main()

If your instructor gave you this template, you need a new instructor.
In C, main returns int.

i dont believe that .

Then find out for yourself, by reading the relevant language definition
specification, ISO/IEC 9899.

my c/c++ teacher (very experienced programmer)

Perhaps he is, but he doesn't know much about C if he can't even get the
entry point right.

AND the book were using both say that if main does not return a
value it can be declared void !

Then get a better book. Better still, get ISO/IEC 9899.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Martin Ambuhl]

Heinrich Pumpernickel wrote:

On Jul 1, 5:04 am, Richard Heathfield <[e-mail].i nvalidwrote:

>Heinrich Pumpernickel said:

>>void main()

If your instructor gave you this template, you need a new instructor. In
C, main returns int.

i dont believe that . my c/c++ teacher (very experienced programmer)
AND the book were using both say that if main does not return a
value it can be declared void !

As it happens, both your teacher and the author of your book are
incompetent. In both C and C++ (there is no such beast as c/c++) main
in a hosted implementation returns an int. Your book should be burnt.
Your "very experienced" teacher is probably protected from burning. It
is time for you to start learning C (or C++) and not what errors your
teacher is "very experienced" in using.

[deepak]

On Jul 1, 8:23 am, Richard Heathfield <[e-mail].i nvalidwrote:

Heinrich Pumpernickel said:

On Jul 1, 5:04 am, Richard Heathfield <[e-mail].i nvalidwrote:

Heinrich Pumpernickel said:

28b (macros). write a macro, sizeof(var), that returns the size of
its argument .

#define SIZEOF(x) (sizeof(x))

but i m not allowed to do that

you are not allowed, to use the sizeof() operator for this .

Why not? That's what it's *for*.

well its just an excersise

I hope that the point of the exercise is to demonstrate that there is no
satisfactory, portable solution to the problem, other than to change
the rules and allow use of the sizeof operator.

You can just about do it for objects:

#define SIZEOF(x) ((unsigned char *)(&(x)+1)-((unsigned char *)&(x))

#define SIZEOF(x) (&x + 1) -(&x)
It will not work?
Please correct me If I'm wrong.

>
but you can't do it for expressions or types without relying on
undefined behaviour, which is never wise if you can avoid it, and here
it can be avoided with ease by using sizeof.

given is the following template....... ...

<snip>

void main()

If your instructor gave you this template, you need a new instructor.
In C, main returns int.

i dont believe that .

Then find out for yourself, by reading the relevant language definition
specification, ISO/IEC 9899.

my c/c++ teacher (very experienced programmer)

Perhaps he is, but he doesn't know much about C if he can't even get the
entry point right.

AND the book were using both say that if main does not return a
value it can be declared void !

Then get a better book. Better still, get ISO/IEC 9899.

--
Richard Heathfield <http://www.cpax.org.uk >
Email: -www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999- Hide quoted text -

- Show quoted text -

[J. J. Farrell]

On Jun 30, 8:15 pm, Heinrich Pumpernickel <lan...@linuxma il.org>
wrote:

On Jul 1, 5:04 am, Richard Heathfield <[e-mail].i nvalidwrote:

Heinrich Pumpernickel said:

given is the following template....... ...

void main()

If your instructor gave you this template, you need a new instructor. In
C, main returns int.

i dont believe that .

Well, bully for you. Lots of people refuse to believe facts, but that
doesn't alter the facts.

my c/c++ teacher (very experienced programmer)
AND the book were using both say that if main does not return a
value it can be declared void !

Then you need to change your books as well as your teacher. C is well
defined by ISO Standards; it doesn't matter what nonsense is contained
in books which claims to be about C.

[Denis Kasak]

deepak wrote:

>>On Jul 1, 5:04 am, Richard Heathfield <[e-mail].i nvalidwrote:

I hope that the point of the exercise is to demonstrate that there is no
satisfactory , portable solution to the problem, other than to change
the rules and allow use of the sizeof operator.

You can just about do it for objects:

#define SIZEOF(x) ((unsigned char *)(&(x)+1)-((unsigned char *)&(x))

#define SIZEOF(x) (&x + 1) -(&x)
It will not work?
Please correct me If I'm wrong.

No. Apart from the fact that your macro would still only work for
objects, as Richard already pointed out, it would also always evaluate
to 1. This is a consequence of the way pointer arithmetics work
(semantically, the subtraction of pointers gives you the number of
objects of the type of x which could fit between those two pointers).
sizeof returns the size of the object in bytes and since 'byte' and
'char' are synonyms in C, subtracting char pointers evaluates to the
number of bytes which could fit between them (in this case, the size of
the object).

--
Denis Kasak

[Flash Gordon]

J. J. Farrell wrote, On 01/07/07 07:31:

On Jun 30, 8:15 pm, Heinrich Pumpernickel <lan...@linuxma il.org>
wrote:

>On Jul 1, 5:04 am, Richard Heathfield <[e-mail].i nvalidwrote:

>>Heinrich Pumpernickel said:
given is the following template....... ...
void main()
If your instructor gave you this template, you need a new instructor. In
C, main returns int.

i dont believe that .

Well, bully for you. Lots of people refuse to believe facts, but that
doesn't alter the facts.

It is understandable the a student would be more inclined to be believe
his teacher and text book than a random collection of people on the
internet.

>my c/c++ teacher (very experienced programmer)
AND the book were using both say that if main does not return a
value it can be declared void !

Then you need to change your books as well as your teacher. C is well
defined by ISO Standards; it doesn't matter what nonsense is contained
in books which claims to be about C.

True. Also checking the relevant section of the comp.lang.c FAQ at
http://c-faq.com specifically http://c-faq.com/ansi/voidmain.html

Note that the further reading page includes a link to a post by
P.J.Plauger who is an author of a book on C, an author of standard C
libraries, and I think was on the committee that standardised C, so he
knows what he speaks of.

You can look at drafts of the C standards yourself, follow this link for
more details http://clc-wiki.net/wiki/c_standard
--
Flash Gordon

[Army1987]

"Richard Heathfield" <rj*@see.sig.in validha scritto nel messaggio news:-8************** *************** *@bt.com...

Heinrich Pumpernickel said:

>On Jul 1, 5:04 am, Richard Heathfield <[e-mail].i nvalidwrote:

>>Heinrich Pumpernickel said:

28b (macros). write a macro, sizeof(var), that returns the size of
its argument .

#define SIZEOF(x) (sizeof(x))

but i m not allowed to do that

>>>
you are not allowed, to use the sizeof() operator for this .

Why not? That's what it's *for*.

well its just an excersise

I hope that the point of the exercise is to demonstrate that there is no
satisfactory, portable solution to the problem, other than to change
the rules and allow use of the sizeof operator.

You can just about do it for objects:

#define SIZEOF(x) ((unsigned char *)(&(x)+1)-((unsigned char *)&(x))

I've tried
#define SIZEOF(x) ((unsigned char*)(&(x)+1)-((unsigned char*)&(x))
#include <stdio.h>
int main(void)
{
register int x = 23;
printf("%d %d\n", (int)sizeof(x), (int)SIZEOF(x)) ;
return 0;
}
on my DS9K, and something very strange happened...