pragma once

[Jacob Jensen]

Hi

I have a problem creating C++ code that is multiplatform compilable. My
problem is using the "#pragma once" directive which can be used by microsoft
Visual Studio pre-compiler but which gives warnings when used by gcc for
example. I would like to use it when compiling with Visual C++ compiler, but
how can I create a smart macro or something, so that it is truly ignored
when compiler with gcc. I have tried the following which actually dose not
serve my wish:

1-
#ifdef VISUAL_STUDIO_C OMPILER
#define MY_ONCE once
#else
#define MY_ONCE
#endif

and then to use it I simply type:
#pragma MY_ONCE

But this still gives a warning when compiled with gcc with the -Wall option
given.

2-
In a pragma_once.h file I type the following
#ifdef VISUAL_STUDIO_C OMPILER
#pragma once
#endif

And then whenever i need it I include pragma_once.h. The problem with this
is that it does not work, since pragma once directive is only effective for
the file it is located in, in this case pragma_once.h

3-
I do not have any other ideas but define a macro in some way as below:
#ifdef VISUAL_STUDIO_C OMPILER
#define PRAGMA_ONCE "#pragma once"
#else
#define PRAGMA_ONCE
#endif

but this does not compile, and I found it impossible to compile it with
similar structures.

[Guest]

Re: pragma once

Dont use microsoft specific things

Use
-----------------
#ifndef __MY_HEADER_FIL E_H__
#define __MY_HEADER_FIL E_H__

// my code here

#endif // __MY_HEADER_FIL E_H__
-----------------
instead of
-----------------
#pragma once

// my code here
-----------------

[Jacob Jensen]

Re: pragma once

But I want to use the pragma once directive with my microsoft compiler. Is
there no other option in to your knowledge?

Thank you again in advance
Jacob

"<- Chameleon ->" <cham_gss@hotma il.NOSPAM.com> wrote in message
news:c4m182$e5v $1@nic.grnet.gr ...[color=blue]
> Dont use microsoft specific things
>
> Use
> -----------------
> #ifndef __MY_HEADER_FIL E_H__
> #define __MY_HEADER_FIL E_H__
>
> // my code here
>
> #endif // __MY_HEADER_FIL E_H__
> -----------------
> instead of
> -----------------
> #pragma once
>
> // my code here
> -----------------
>
>[/color]

[Jacob Jensen]

Re: pragma once

But I want to use the pragma once directive with my microsoft compiler. Is
there no other option in to your knowledge?

Thank you again in advance
Jacob

"<- Chameleon ->" <cham_gss@hotma il.NOSPAM.com> wrote in message
news:c4m182$e5v $1@nic.grnet.gr ...[color=blue]
> Dont use microsoft specific things
>
> Use
> -----------------
> #ifndef __MY_HEADER_FIL E_H__
> #define __MY_HEADER_FIL E_H__
>
> // my code here
>
> #endif // __MY_HEADER_FIL E_H__
> -----------------
> instead of
> -----------------
> #pragma once
>
> // my code here
> -----------------
>
>[/color]

[Guest]

Re: pragma once

> But I want to use the pragma once directive with my microsoft compiler. Is[color=blue]
> there no other option in to your knowledge?[/color]

in this case try this: (_MSC_VER)
I think I saw it inside gl.h (OpenGL header)
UNTESTED
[color=blue][color=green]
> > -----------------[/color][/color]
#ifdef _MSC_VER[color=blue][color=green]
> > #pragma once[/color][/color]
#endif[color=blue][color=green]
> >
> > // my code here
> > -----------------
> >
> >[/color]
>
>[/color]

[Heinz Ozwirk]

Re: pragma once

"Jacob Jensen" <jacob_news_dkN oSpaaaammmm@yah oo.co.uk> schrieb im Newsbeitrag news:nCBbc.430$ KX.319@news.get 2net.dk...
: But I want to use the pragma once directive with my microsoft compiler. Is
: there no other option in to your knowledge?

If you really want to use #pragma once, do it as Microsoft does:

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

HTH
Heinz

[Guest]

Re: pragma once

> But I want to use the pragma once directive with my microsoft compiler. Is[color=blue]
> there no other option in to your knowledge?[/color]

in this case try this: (_MSC_VER)
I think I saw it inside gl.h (OpenGL header)
UNTESTED
[color=blue][color=green]
> > -----------------[/color][/color]
#ifdef _MSC_VER[color=blue][color=green]
> > #pragma once[/color][/color]
#endif[color=blue][color=green]
> >
> > // my code here
> > -----------------
> >
> >[/color]
>
>[/color]

[Heinz Ozwirk]

Re: pragma once

"Jacob Jensen" <jacob_news_dkN oSpaaaammmm@yah oo.co.uk> schrieb im Newsbeitrag news:nCBbc.430$ KX.319@news.get 2net.dk...
: But I want to use the pragma once directive with my microsoft compiler. Is
: there no other option in to your knowledge?

If you really want to use #pragma once, do it as Microsoft does:

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

HTH
Heinz

[Julie]

Re: pragma once

"<- Chameleon ->" wrote:[color=blue]
> Use
> -----------------
> #ifndef __MY_HEADER_FIL E_H__
> #define __MY_HEADER_FIL E_H__[/color]

Double-underscore identifiers are reserved for implementation purposes. Use
something like:

#define MY_HEADER_FILE_ H

instead.

[Julie]

Re: pragma once

"<- Chameleon ->" wrote:[color=blue]
> Use
> -----------------
> #ifndef __MY_HEADER_FIL E_H__
> #define __MY_HEADER_FIL E_H__[/color]

Double-underscore identifiers are reserved for implementation purposes. Use
something like:

#define MY_HEADER_FILE_ H

instead.

[Kevin Goodsell]

Re: pragma once

<- Chameleon -> wrote:
[color=blue]
> Dont use microsoft specific things
>
> Use
> -----------------
> #ifndef __MY_HEADER_FIL E_H__
> #define __MY_HEADER_FIL E_H__[/color]

No, don't use this. Not if you want well-defined code.

17.4.3.1.2 Global names [lib.global.name s]

1 Certain sets of names and function signatures are always reserved to
the implementation:

--Each name that contains a double underscore __) or begins with an
underscore followed by an uppercase letter (_lex.key_) is reserved
to the implementation for any use.

In short, don't use identifiers that begin with an underscore or contain
a sequence of 2 underscores unless you really know what you are doing.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

[Cy Edmunds]

Re: pragma once

"Jacob Jensen" <jacob_news_dkN oSpaaaammmm@yah oo.co.uk> wrote in message
news:nCBbc.430$ KX.319@news.get 2net.dk...[color=blue]
> But I want to use the pragma once directive with my microsoft compiler.[/color]

This seems like a very strange requirement. Why?

--
Cy

http://home.rochester.rr.com/cyhome/

[Cy Edmunds]

Re: pragma once

"Julie" <julie@nospam.c om> wrote in message
news:406F02C5.2 83F6763@nospam. com...[color=blue]
> "<- Chameleon ->" wrote:[color=green]
> > Use
> > -----------------
> > #ifndef __MY_HEADER_FIL E_H__
> > #define __MY_HEADER_FIL E_H__[/color]
>
> Double-underscore identifiers are reserved for implementation purposes.[/color]
Use[color=blue]
> something like:
>
> #define MY_HEADER_FILE_ H
>
> instead.[/color]

Indeed. Even a single leading underscore followed by a capital letter is
reserved for implementors. Instead of remembering all these arcane rules,
best not to use leading underscores at all.

--
Cy

http://home.rochester.rr.com/cyhome/

[Kevin Goodsell]

Re: pragma once

<- Chameleon -> wrote:
[color=blue]
> Dont use microsoft specific things
>
> Use
> -----------------
> #ifndef __MY_HEADER_FIL E_H__
> #define __MY_HEADER_FIL E_H__[/color]

No, don't use this. Not if you want well-defined code.

17.4.3.1.2 Global names [lib.global.name s]

1 Certain sets of names and function signatures are always reserved to
the implementation:

--Each name that contains a double underscore __) or begins with an
underscore followed by an uppercase letter (_lex.key_) is reserved
to the implementation for any use.

In short, don't use identifiers that begin with an underscore or contain
a sequence of 2 underscores unless you really know what you are doing.

-Kevin
--
My email address is valid, but changes periodically.
To contact me please use the address from a recent posting.

[Cy Edmunds]

Re: pragma once

"Jacob Jensen" <jacob_news_dkN oSpaaaammmm@yah oo.co.uk> wrote in message
news:nCBbc.430$ KX.319@news.get 2net.dk...[color=blue]
> But I want to use the pragma once directive with my microsoft compiler.[/color]

This seems like a very strange requirement. Why?

--
Cy

http://home.rochester.rr.com/cyhome/