Understanding callback

**Keith Thompson** · Nov 1 '08, 08:05 PM

Re: Understanding callback

kid joe <spamtrap@spamt rap.invalidwrit es:

I have seen the WndProc prototyped two ways,
>
LONG WINAPI WndProc ( .... );
and
LRESULT CALLBACK WndProc ( .... );
>
Are these functionally equivalent?
What are WINAPI and CALLBACK defined as?
Why are there two ways to go about this?

These are specific to Windows. You'll get much better information
if you post to comp.os.ms-windows.program mer.win32.

And please use a shorter signature.

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

**jacob navia** · Nov 1 '08, 09:15 PM

Re: Understanding callback

kid joe wrote:

Hello,
>
I have seen the WndProc prototyped two ways,
>
LONG WINAPI WndProc ( .... );
and
LRESULT CALLBACK WndProc ( .... );
>
Are these functionally equivalent?

Under 32 bit windows they are equivalent.
Under 64 bit windows they are not since LRESULT
is a 64 bit type and LONG is a 32 bit type...

What are WINAPI and CALLBACK defined as?

WINAPI is _stdcall in 32 Bit windows
CALLBACK is also defined as _stdcall.

Under 64 bit windows _stdcall doesn't exist
so both definitions are equivalent too,
probably defined as nothing.

--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique

403 Forbidden

http://www.cs.virginia.edu/~lcc-win32

**kid joe** · Nov 1 '08, 09:45 PM

Re: Understanding callback

On Sat, 01 Nov 2008 22:13:40 +0100, jacob navia wrote:

kid joe wrote:

>Hello,
>>
>I have seen the WndProc prototyped two ways,
>>
>LONG WINAPI WndProc ( .... );
>and
>LRESULT CALLBACK WndProc ( .... );
>>
>Are these functionally equivalent?

>
Under 32 bit windows they are equivalent.
Under 64 bit windows they are not since LRESULT
is a 64 bit type and LONG is a 32 bit type...
>
>

>What are WINAPI and CALLBACK defined as?

>
WINAPI is _stdcall in 32 Bit windows
CALLBACK is also defined as _stdcall.
>
Under 64 bit windows _stdcall doesn't exist
so both definitions are equivalent too,
probably defined as nothing.

Thanks a lot for the info.

I guess the only remaining question is, why are there these two different
prototypes for the same function, even if they're functionally equivalent?

Joe

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\ .. \\ |`-'|`-, /
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\)\)\\ `-' `-'
`

**Pawel Dziepak** · Nov 1 '08, 09:55 PM

Re: Understanding callback

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

kid joe wrote:

I guess the only remaining question is, why are there these two different
prototypes for the same function, even if they're functionally equivalent?

Despite the fact that implementation is the same, semantic is different.
CALLBACK informs that it is callback function (called from winapi
libraries). LRESULT stands for long type that stores function's return
value. WINAPI is used for functions that are part of WinAPI. LONG is
just kind of type (that probably has the same size on all platforms).

MSDN states that the correct prototype is:
LRESULT CALLBACK WindowProc(...) ;
What fits my explanation of CALLBACK, WINAPI, LONG and LRESULT semantics.

These definitions allows to change implementation or hardware platform
without breaking API compliance.

Pawel Dziepak

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Version: GnuPG v1.4.9 (GNU/Linux)
Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org

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**Ian Collins** · Nov 1 '08, 09:55 PM

Re: Understanding callback

kid joe wrote:

>
I guess the only remaining question is, why are there these two different
prototypes for the same function, even if they're functionally equivalent?
>

A windows group would be the place to ask.

Please don't post such a daft, ill-formed signature.

--
Ian Collins

**CBFalconer** · Nov 2 '08, 12:45 AM

Re: Understanding callback

Ian Collins wrote:

kid joe wrote:
>

>I guess the only remaining question is, why are there these two
>different prototypes for the same function, even if they're
>functionally equivalent?

>
A windows group would be the place to ask.
>
Please don't post such a daft, ill-formed signature.

He ignored the same request posted about 2 hours before his last
entry. If he continues again I guess the only solution is the
plonk file. Besides, his queries are all off-topic. He might read
the following references:

Some useful references about C:
<http://www.ungerhu.com/jxh/clc.welcome.txt >
<http://c-faq.com/ (C-faq)
<http://benpfaff.org/writings/clc/off-topic.html>
<http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf(C99)
<http://cbfalconer.home .att.net/download/n869_txt.bz2 (pre-C99)
<http://www.dinkumware. com/c99.aspx (C-library}
<http://gcc.gnu.org/onlinedocs/ (GNU docs)
<http://clc-wiki.net/wiki/C_community:com p.lang.c:Introd uction>

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.

**Default User** · Nov 2 '08, 06:15 AM

Re: Understanding callback

Keith Thompson wrote:

And please use a shorter signature.

Or at the very least a legal signature separator.

Brian

**George** · Nov 2 '08, 07:55 AM

Re: Understanding callback

On Sat, 01 Nov 2008 22:13:40 +0100, jacob navia wrote:

kid joe wrote:

>Hello,
>>
>I have seen the WndProc prototyped two ways,
>>
>LONG WINAPI WndProc ( .... );
>and
>LRESULT CALLBACK WndProc ( .... );
>>
>Are these functionally equivalent?

>
Under 32 bit windows they are equivalent.
Under 64 bit windows they are not since LRESULT
is a 64 bit type and LONG is a 32 bit type...
>
>

>What are WINAPI and CALLBACK defined as?

>
WINAPI is _stdcall in 32 Bit windows
CALLBACK is also defined as _stdcall.
>
Under 64 bit windows _stdcall doesn't exist
so both definitions are equivalent too,
probably defined as nothing.

But it's not just windows stuff.

There is an aspect of callback functions that is

a) metasyntactic
b) relevant to standard C
--
George

Hundreds of thousands of American servicemen and women are deployed across
the world in the war on terror. By bringing hope to the oppressed, and
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**Wolfgang Draxinger** · Nov 2 '08, 03:55 PM

Re: Understanding callback

Default User wrote:

Keith Thompson wrote:
>
>

>And please use a shorter signature.

>
Or at the very least a legal signature separator.

And if the OP wonders how that looks like: It's
"-- \n", i.e. 2 dashes, 1 space 1 newline.

Wolfgang Draxinger
--
E-Mail address works, Jabber: hexarith@jabber .org, ICQ: 134682867

**kid joe** · Nov 2 '08, 10:45 PM

Re: Understanding callback

Got it, thanks. I guess just not worry about it in practise...

Joe

PS. For people who had problems with my sig, try using a fixed-width font
(i.e. Courier New) - I think you'll like it :-)

On Sat, 01 Nov 2008 22:52:21 +0100, Pawel Dziepak wrote:

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
>
kid joe wrote:

>I guess the only remaining question is, why are there these two different
>prototypes for the same function, even if they're functionally equivalent?

>
Despite the fact that implementation is the same, semantic is different.
CALLBACK informs that it is callback function (called from winapi
libraries). LRESULT stands for long type that stores function's return
value. WINAPI is used for functions that are part of WinAPI. LONG is
just kind of type (that probably has the same size on all platforms).
>
MSDN states that the correct prototype is:
LRESULT CALLBACK WindowProc(...) ;
What fits my explanation of CALLBACK, WINAPI, LONG and LRESULT semantics.
>
These definitions allows to change implementation or hardware platform
without breaking API compliance.
>
Pawel Dziepak
>
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Version: GnuPG v1.4.9 (GNU/Linux)
Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org
>
iEYEARECAAYFAkk Mz5UACgkQPFW+cU iIHNrMVwCfSOOdF s3m1lMnNYDvtzfn MMWS
NgwAn1JPmkDB7Zk vrPFrAlvNSD6GH6 Rk
=sDyQ
-----END PGP SIGNATURE-----

--
.--------------------.
| |
| Good Evening.... | .--.--.
| | .; .;|;. ;.
`-------------. ,---' .;_;' `;_;.
\| ; ;' `; ;
\ ;;'.--.___.--.`;;
;-( o )=3D( o )-;
( `--' | `--' )
\| . . |/
........... . .:::::. . .______
/ . '---` . '\
.' `. .' \
| ____,.- . | `.....' | _______ |
| ,-' \ /|\'' \.-- |
| / \.'\ /,'. \. - |
| /| ` `\ / \ |
| ,/ _ '/ '\ |
,-' ,-. |o '
/ '| | | | \
/ ,/| |o | \ `
| .' | |.' |. \ \
________/ .'____|________ _______________ _||__`. `__________
( \ ) / )
'-. '-. ( .-` .-`
'-. .-'--.__. .-.__.--`-. .-`
'-..' \--' : ~`:=3D,`- `..-`
\ .. \\ |`-'|`-, /
\\\\\\\) | |`-'/.'/
\)\)\\ `-' `-'
`

**James Kuyper** · Nov 2 '08, 10:55 PM

Re: Understanding callback

kid joe wrote:

Got it, thanks. I guess just not worry about it in practise...
>
Joe
>
PS. For people who had problems with my sig, try using a fixed-width font
(i.e. Courier New) - I think you'll like it :-)

Using Courier New didn't make your signature 90% shorter, which is the
main thing that needs to be fixed.

**Keith Thompson** · Nov 3 '08, 01:35 AM

Re: Understanding callback

kid joe <spamtrap@spamt rap.invalidwrit es:

Got it, thanks. I guess just not worry about it in practise...
>
Joe
>
PS. For people who had problems with my sig, try using a fixed-width font
(i.e. Courier New) - I think you'll like it :-)

[...]

I use a fixed-width font. The ASCII art you use as a signature is
reasonably impressive as ASCII art, but it's *way* too long as a
signature. The usual guideline (and I think this may be mentioned in
one of the RFCs) is that a signature should be no more than 4 lines,
not including the "-- " delimiter.

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
Nokia
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

**Nick Keighley** · Nov 3 '08, 09:15 AM

Re: Understanding callback

George wrote:

On Sat, 01 Nov 2008 22:13:40 +0100, jacob navia wrote:

kid joe wrote:

I have seen the WndProc prototyped two ways,
>
LONG WINAPI WndProc ( .... );
and
LRESULT CALLBACK WndProc ( .... );
>
Are these functionally equivalent?

Under 32 bit windows they are equivalent.
Under 64 bit windows they are not since LRESULT
is a 64 bit type and LONG is a 32 bit type...

What are WINAPI and CALLBACK defined as?

WINAPI is _stdcall in 32 Bit windows
CALLBACK is also defined as _stdcall.

Under 64 bit windows _stdcall doesn't exist
so both definitions are equivalent too,
probably defined as nothing.

>
But it's not just windows stuff.
>
There is an aspect of callback functions that is
>
a) metasyntactic
b) relevant to standard C

he wasn't asking about callbacks though. He was asking specific
windows related questions that could only be answered by knowing about
various MS typedefs.

and what do you mean by "metasyntactic" ?
Is that like Post Modernism?

--
Nick Keighley

**CBFalconer** · Nov 3 '08, 10:15 PM

Re: Understanding callback

kid joe wrote:

>
Got it, thanks. I guess just not worry about it in practise...
>
PS. For people who had problems with my sig, try using a
fixed-width font (i.e. Courier New) - I think you'll like it :-)

Since you ignore requests about your sig, and also top-post, you
have won an entry in the PLONK file. Goodbye.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home .att.net>
Try the download section.