main function address

**Joona I Palaste** · Nov 14 '05, 05:33 AM

Re: main function address

Sweety <sweety_elegant @yahoo.co.in> scribbled the following:[color=blue]
> hi,
> Is main function address is 657.
> its show in all compiler.
> try it & say why?
> bye,[/color]

No, the main function's address may be whatever your implementation
wants it to be. You can't rely on it being any particular numeric value,
actually you can't rely it on being a numeric value at all.

--
/-- Joona Palaste (palaste@cc.hel sinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"Keep shooting, sooner or later you're bound to hit something."
- Misfire

**Old Wolf** · Nov 14 '05, 05:33 AM

Re: main function address

Dan.Pop@cern.ch (Dan Pop) wrote:[color=blue]
>
> The easy way out for printf would be something like %q which expects a
> pointer to a void function taking no arguments. However, given that %p
> itself is virtually never used in real world programs, and that
> %lx or %llx do work on the pointer converted to the appropriate integer
> type, there is little point on adding %q.[/color]

%p is indispensable[*] on systems without flat address space
(for example, on MS-DOS it prints segment:offset, on 8051 it tells you
which page the pointer points to, and presumably on these "semi-64 bit"
contraptions that are coming out, it will print segment:offset) .
Admittedly I've never used it except in recording of debug information.

Windows 3.1 crash messages printed their addresses in the same format,
so I would conjecture that Windows still uses "%p" to print the
address of where programs crashed (virtually every day, in real world PCs)
[*] Of course you can do the (unsigned char *)&ptr thing but that is tedious,
and using %lx is relying on undefined behaviour.

**Lew Pitcher** · Nov 14 '05, 05:33 AM

Re: main function address

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Sweety wrote:
| hi,
| Is main function address is 657.

Perhaps, perhaps not. It depends on your compiler, linker, operating system, and
CPU.

| its show in all compiler.

No, it doesn't.

~ ~/code $ cat printmain.c
~ #include <stdio.h>
~ #include <stdlib.h>

~ int main(void)
~ {
~ printf("main() at %p\n",(void *)&main);

~ return EXIT_SUCCESS;
~ }

~ ~/code $ cc -o printmain printmain.c

~ ~/code $ printmain
~ main() at 0x8048328

~ ~/code $

| try it & say why?

I did, and it' didn't, so I can't say why 657.

| bye,

- --
Lew Pitcher

Master Codewright & JOAT-in-training | GPG public key available on request
Registered Linux User #112576 (http://counter.li.org/)
Slackware - Because I know what I'm doing.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.4 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFAc16aagV FX4UWr64RAvsiAJ 9Tq3RBO4marGAqz 3RWYxjcebFfuwCg ry/M
5kAKhQe0/0006+/H6+GJp9I=
=qU+e
-----END PGP SIGNATURE-----

**José de Paula** · Nov 14 '05, 05:33 AM

Re: main function address

Em Tue, 06 Apr 2004 21:51:22 -0400, Lew Pitcher escreveu:
<snip>[color=blue]
> ~ printf("main() at %p\n",(void *)&main);[/color]
<snip>

Wouldn't simply
printf("main() at %p\n", (void *)main);
do? Notice the prunning of the & operator. For what I know,
the name of a function is a pointer to that function, am I right?

--
José de Paula Rodrigues Neto Assis Linux User 175920
Brasília - DF - Brasil counter.li.org

**Lew Pitcher** · Nov 14 '05, 05:33 AM

Re: main function address

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

José de Paula wrote:
| Em Tue, 06 Apr 2004 21:51:22 -0400, Lew Pitcher escreveu:
| <snip>
|
|>~ printf("main() at %p\n",(void *)&main);
|
| <snip>
|
| Wouldn't simply
| printf("main() at %p\n", (void *)main);
| do? Notice the prunning of the & operator. For what I know,
| the name of a function is a pointer to that function, am I right?

You are correct. The & was unnecessary.

- --
Lew Pitcher

Master Codewright & JOAT-in-training | GPG public key available on request
Registered Linux User #112576 (http://counter.li.org/)
Slackware - Because I know what I'm doing.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.4 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFAc2o1agV FX4UWr64RAofEAK CScgoEuAKn8ci/cjeimsG01iyWXAC gznfY
/2jtHAGq0Fpm6dHK Z1ZdP7E=
=ra40
-----END PGP SIGNATURE-----

**Dan Pop** · Nov 14 '05, 05:33 AM

Re: main function address

In <843a4f78.04041 41850.166ab63b@ posting.google. com> oldwolf@inspire .net.nz (Old Wolf) writes:
[color=blue]
>Dan.Pop@cern.c h (Dan Pop) wrote:[color=green]
>>
>> The easy way out for printf would be something like %q which expects a
>> pointer to a void function taking no arguments. However, given that %p
>> itself is virtually never used in real world programs, and that
>> %lx or %llx do work on the pointer converted to the appropriate integer
>> type, there is little point on adding %q.[/color]
>
>%p is indispensable[*] on systems without flat address space
>(for example, on MS-DOS it prints segment:offset, on 8051 it tells you
>which page the pointer points to, and presumably on these "semi-64 bit"
>contraptions that are coming out, it will print segment:offset) .
>Admittedly I've never used it except in recording of debug information.
>
>Windows 3.1 crash messages printed their addresses in the same format,
>so I would conjecture that Windows still uses "%p" to print the
>address of where programs crashed (virtually every day, in real world PCs)[/color]

Have I ever advocating dropping %p from the standard? If not, what
exactly is your point?
[color=blue]
>[*] Of course you can do the (unsigned char *)&ptr thing but that is tedious,
>and using %lx is relying on undefined behaviour.[/color]

You got it wrong: using %p for function pointers *is* relying on undefined
behaviour, using %lx for function pointers converted to unsigned long is
NOT undefined behaviour (such conversions are *explicitly* allowed by the
standard).

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Dan.Pop@ifh.de

**E. Robert Tisdale** · Nov 14 '05, 05:33 AM

Re: main function address

Lew Pitcher wrote:
[color=blue]
> Sweety wrote:
> |
> | Is main function address is 657.
>
> Perhaps, perhaps not.
> It depends on your compiler, linker, operating system, and CPU.
>
> | its show in all compiler.
>
> No, it doesn't.
>
> ~ ~/code $ cat printmain.c
> ~ #include <stdio.h>
> ~ #include <stdlib.h>
>
> ~ int main(void)
> ~ {
> ~ printf("main() at %p\n",(void *)&main);
>
> ~ return EXIT_SUCCESS;
> ~ }
>
> ~ ~/code $ cc -o printmain printmain.c
>
> ~ ~/code $ printmain
> ~ main() at 0x8048328
>
> ~ ~/code $
>
>
> | try it & say why?
>
> I did, and it' didn't, so I can't say why 657.[/color]
[color=blue]
> cat printmain.c[/color]
#include <stdio.h>
#include <stdlib.h>

int main(void) {
printf("main() at %p\n",(void *)&main);

return EXIT_SUCCESS;
}
[color=blue]
> gcc -Wall -std=c99 -pedantic -o printmain printmain.c
> ./printmain[/color]
main() at 0x8048328

Why 0x8048328? :-)

**E. Robert Tisdale** · Nov 14 '05, 05:33 AM

Re: main function address

José de Paula wrote:
[color=blue]
> Lew Pitcher escreveu:
>
> <snip>[color=green]
>>~ printf("main() at %p\n",(void *)&main);[/color]
> <snip>
>
> Wouldn't simply[/color]
[color=blue]
> printf("main() at %p\n", (void *)main);[/color]
[color=blue]
> do? Notice the pruning of the & operator. For what I know,
> the name of a function is a pointer to that function. Am I right?[/color]

Yes. There is an implicit conversion
from the name of a function to a pointer to the function.

**Martin Dickopp** · Nov 14 '05, 05:34 AM

Re: main function address

Lew Pitcher <lpitcher@sympa tico.ca> writes:
[color=blue]
> #include <stdio.h>
> #include <stdlib.h>
>
> int main(void)
> {
> printf("main() at %p\n",(void *)&main);
>
> return EXIT_SUCCESS;
> }[/color]

Is the cast to `void *' valid? I cannot find anything in the standard
which allows a pointer to a function to be converted to type `void *'.

Martin

--
,--. Martin Dickopp, Dresden, Germany ,= ,-_-. =.
/ ,- ) http://www.zero-based.org/ ((_/)o o(\_))
\ `-' `-'(. .)`-'
`-. Debian, a variant of the GNU operating system. \_/

**pete** · Nov 14 '05, 05:34 AM

Re: main function address

Martin Dickopp wrote:[color=blue]
>
> Lew Pitcher <lpitcher@sympa tico.ca> writes:
>[color=green]
> > #include <stdio.h>
> > #include <stdlib.h>
> >
> > int main(void)
> > {
> > printf("main() at %p\n",(void *)&main);
> >
> > return EXIT_SUCCESS;
> > }[/color]
>
> Is the cast to `void *' valid?[/color]

No.

In N869, it's one of the common extensions.

J.5.7 Function pointer casts
[#2] A pointer to a function may be cast to a pointer to an
object or to void, allowing a function to be inspected or
modified (for example, by a debugger) (6.5.4).

.... which makes it more obviously not part of standard C.

--
pete

**Vijay Kumar R Zanvar** · Nov 14 '05, 05:34 AM

Re: main function address

"Lew Pitcher" <lpitcher@sympa tico.ca> wrote in message news:W6Jcc.5205 $BF2.654200@new s20.bellglobal. com...[color=blue]
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Sweety wrote:
> | hi,
> | Is main function address is 657.
>
> Perhaps, perhaps not. It depends on your compiler, linker, operating system, and
> CPU.
>
> | its show in all compiler.
>
> No, it doesn't.
>
> ~ ~/code $ cat printmain.c
> ~ #include <stdio.h>
> ~ #include <stdlib.h>
>
> ~ int main(void)
> ~ {
> ~ printf("main() at %p\n",(void *)&main);
>
> ~ return EXIT_SUCCESS;
> ~ }
>
> ~ ~/code $ cc -o printmain printmain.c
>
> ~ ~/code $ printmain
> ~ main() at 0x8048328
>[/color]

F:\Vijay\C> bcc32 printmain.c
F:\Vijay\C> printmain
main() at 00401150

F:\Vijay\C> gcc printmain.c
F:\Vijay\C> a
main() at 15ee

**Keith Thompson** · Nov 14 '05, 05:34 AM

Re: main function address

Lew Pitcher <lpitcher@sympa tico.ca> writes:[color=blue]
> José de Paula wrote:
> | Em Tue, 06 Apr 2004 21:51:22 -0400, Lew Pitcher escreveu:
> | <snip>
> |
> |>~ printf("main() at %p\n",(void *)&main);
> |
> | <snip>
> |
> | Wouldn't simply
> | printf("main() at %p\n", (void *)main);
> | do? Notice the prunning of the & operator. For what I know,
> | the name of a function is a pointer to that function, am I right?
>
> You are correct. The & was unnecessary.[/color]

It's unnecessary, but harmless, and some might argue that it's
clearer, since it makes it more explicit that the expression is an
address.

A function name is implicitly converted to a function pointer unless
it's the operand of a sizeof or unary & operator. (In the case of
sizeof, the resulting expression is illegal.)

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
Schroedinger does Shakespeare: "To be *and* not to be"

**Richard Bos** · Nov 14 '05, 05:34 AM

Re: main function address

Martin Dickopp <expires-2004-05-31@zero-based.org> wrote:
[color=blue]
> Lew Pitcher <lpitcher@sympa tico.ca> writes:
>[color=green]
> > #include <stdio.h>
> > #include <stdlib.h>
> >
> > int main(void)
> > {
> > printf("main() at %p\n",(void *)&main);
> >
> > return EXIT_SUCCESS;
> > }[/color]
>
> Is the cast to `void *' valid?[/color]

No. Mind you, there is no better way to print the address of a function,
either. Where this works, it works; where it doesn't, nothing else is
likely to.

Richard

**Lew Pitcher** · Nov 14 '05, 05:34 AM

Re: main function address

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

pete wrote:
| Martin Dickopp wrote:
|
|>Lew Pitcher <lpitcher@sympa tico.ca> writes:
|>
|>
|>>#include <stdio.h>
|>>#include <stdlib.h>
|>>
|>>int main(void)
|>>{
|>> printf("main() at %p\n",(void *)&main);
|>>
|>> return EXIT_SUCCESS;
|>>}
|>
|>Is the cast to `void *' valid?
|
|
| No.
|
| In N869, it's one of the common extensions.
|
| J.5.7 Function pointer casts
| [#2] A pointer to a function may be cast to a pointer to an
| object or to void, allowing a function to be inspected or
| modified (for example, by a debugger) (6.5.4).
|
| ... which makes it more obviously not part of standard C.

In 9989-1999 (admittedly, just the draft C99 standard, and not the
/actual standard itself), the printf() function documentation in
7.19.6.3 refers the reader to the fprintf() documentation for a
description of it's input. The fprintf() documentation in 7.19.6.1 says
of the %p format

~ p The argument shall be a pointer to void. The value of the pointer is
~ converted to a sequence of printing characters, in an
~ implementation-defined manner.

So, to satisfy the %p format character, the argument to
fprintf()/printf() /must/ be a "pointer to void". Since main is a
"pointer to function returning int", and not a "pointer to void", I
interpreted the documentation as requiring a cast to void pointer.

- --

Lew Pitcher, IT Consultant, Enterprise Application Architecture
Enterprise Technology Solutions, TD Bank Financial Group

(Opinions expressed here are my own, not my employer's)
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.4 (MingW32)

iD8DBQFAc+o1agV FX4UWr64RAgMKAJ 9jpwGgLD0Ib6+Sr FveX/B2DiSkQQCgn1b9
hcqV26vMzT9PW6/myM6CbsQ=
=jmLW
-----END PGP SIGNATURE-----