pragma once

[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/

[Jacob Jensen]

Re: pragma once

For compiler efficiency reasons, that is all. It would be a very nice thing
to have for me, and therefore I would like to find a good solution to my
"problem".


"Cy Edmunds" <cedmunds@spaml ess.rochester.r r.com> wrote in message
news:CkEbc.1010 4$LW2.9792@twis ter.nyroc.rr.co m...[color=blue]
> "Jacob Jensen" <jacob_news_dkN oSpaaaammmm@yah oo.co.uk> wrote in message
> news:nCBbc.430$ KX.319@news.get 2net.dk...[color=green]
> > 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/
>
>[/color]

[Jacob Jensen]

Re: pragma once

For compiler efficiency reasons, that is all. It would be a very nice thing
to have for me, and therefore I would like to find a good solution to my
"problem".


"Cy Edmunds" <cedmunds@spaml ess.rochester.r r.com> wrote in message
news:CkEbc.1010 4$LW2.9792@twis ter.nyroc.rr.co m...[color=blue]
> "Jacob Jensen" <jacob_news_dkN oSpaaaammmm@yah oo.co.uk> wrote in message
> news:nCBbc.430$ KX.319@news.get 2net.dk...[color=green]
> > 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/
>
>[/color]

[Julie]

Re: pragma once

Jacob Jensen wrote:[color=blue]
>
> For compiler efficiency reasons, that is all. It would be a very nice thing
> to have for me, and therefore I would like to find a good solution to my
> "problem".
>
> "Cy Edmunds" <cedmunds@spaml ess.rochester.r r.com> wrote in message
> news:CkEbc.1010 4$LW2.9792@twis ter.nyroc.rr.co m...[color=green]
> > "Jacob Jensen" <jacob_news_dkN oSpaaaammmm@yah oo.co.uk> wrote in message
> > news:nCBbc.430$ KX.319@news.get 2net.dk...[color=darkred]
> > > 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/
> >
> >[/color][/color]

If you are after efficiency (compilation speed?), look into precompiled
headers.

[Julie]

Re: pragma once

Jacob Jensen wrote:[color=blue]
>
> For compiler efficiency reasons, that is all. It would be a very nice thing
> to have for me, and therefore I would like to find a good solution to my
> "problem".
>
> "Cy Edmunds" <cedmunds@spaml ess.rochester.r r.com> wrote in message
> news:CkEbc.1010 4$LW2.9792@twis ter.nyroc.rr.co m...[color=green]
> > "Jacob Jensen" <jacob_news_dkN oSpaaaammmm@yah oo.co.uk> wrote in message
> > news:nCBbc.430$ KX.319@news.get 2net.dk...[color=darkred]
> > > 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/
> >
> >[/color][/color]

If you are after efficiency (compilation speed?), look into precompiled
headers.

[Mike Smith]

Re: pragma once

Jacob Jensen wrote:
[color=blue]
> But I want to use the pragma once directive with my microsoft compiler.[/color]

Why, when there is a perfectly good, cross-platform, widely-used
convention (i.e. include guards) already out there?

--
Mike Smith

[Mike Smith]

Re: pragma once

Jacob Jensen wrote:
[color=blue]
> But I want to use the pragma once directive with my microsoft compiler.[/color]

Why, when there is a perfectly good, cross-platform, widely-used
convention (i.e. include guards) already out there?

--
Mike Smith

[Bill Seurer]

Re: pragma once

Jacob Jensen wrote:
[color=blue]
> For compiler efficiency reasons, that is all. It would be a very nice thing
> to have for me, and therefore I would like to find a good solution to my
> "problem".[/color]

I've looked through all the postings and I'm not clear either what the
problem is or what pragma once does (and, therefore, how it is supposed
to help).

In general pragmas are completely non-portable. Avoid them if at all
possible.

[Bill Seurer]

Re: pragma once

Jacob Jensen wrote:
[color=blue]
> For compiler efficiency reasons, that is all. It would be a very nice thing
> to have for me, and therefore I would like to find a good solution to my
> "problem".[/color]

I've looked through all the postings and I'm not clear either what the
problem is or what pragma once does (and, therefore, how it is supposed
to help).

In general pragmas are completely non-portable. Avoid them if at all
possible.

[Mike Smith]

Re: pragma once

Bill Seurer wrote:
[color=blue]
> Jacob Jensen wrote:
>[color=green]
>> For compiler efficiency reasons, that is all. It would be a very nice
>> thing
>> to have for me, and therefore I would like to find a good solution to my
>> "problem".[/color]
>
>
> I've looked through all the postings and I'm not clear either what the
> problem is or what pragma once does (and, therefore, how it is supposed
> to help).[/color]

#pragma once does more or less exactly what include guards do; i.e.
prevent a header form being included more than once for any given
translation unit. There is no reason whatsoever (except for somewhat
less typing) to use #pragma once instead of include guards.

--
Mike Smith

[Mike Smith]

Re: pragma once

Bill Seurer wrote:
[color=blue]
> Jacob Jensen wrote:
>[color=green]
>> For compiler efficiency reasons, that is all. It would be a very nice
>> thing
>> to have for me, and therefore I would like to find a good solution to my
>> "problem".[/color]
>
>
> I've looked through all the postings and I'm not clear either what the
> problem is or what pragma once does (and, therefore, how it is supposed
> to help).[/color]

#pragma once does more or less exactly what include guards do; i.e.
prevent a header form being included more than once for any given
translation unit. There is no reason whatsoever (except for somewhat
less typing) to use #pragma once instead of include guards.

--
Mike Smith

[Julie]

Re: pragma once

Mike Smith wrote:[color=blue]
> #pragma once does more or less exactly what include guards do; i.e.
> prevent a header form being included more than once for any given
> translation unit. There is no reason whatsoever (except for somewhat
> less typing) to use #pragma once instead of include guards.[/color]

I'd suspect that #pragma once would be more efficient during subsequent
inclusions as the pre-processor could terminate the parse and close the file at
that point.

With an include guard, the entire file must still be parsed.

As I previously mentioned, the best solution for inclusion performance is using
pre-compiled headers.

However, both (#pragma once and pch) are compiler-specific issues, and can be
better answered in a forum dealing with the specifics of the OPs compiler.

The only platform-neutral option is include guards.

[Julie]

Re: pragma once

Mike Smith wrote:[color=blue]
> #pragma once does more or less exactly what include guards do; i.e.
> prevent a header form being included more than once for any given
> translation unit. There is no reason whatsoever (except for somewhat
> less typing) to use #pragma once instead of include guards.[/color]

I'd suspect that #pragma once would be more efficient during subsequent
inclusions as the pre-processor could terminate the parse and close the file at
that point.

With an include guard, the entire file must still be parsed.

As I previously mentioned, the best solution for inclusion performance is using
pre-compiled headers.

However, both (#pragma once and pch) are compiler-specific issues, and can be
better answered in a forum dealing with the specifics of the OPs compiler.

The only platform-neutral option is include guards.