Re: [Boost-users] cross-platfrom binary serialization?

From: Pfligersdorffer, Christian (Christian.Pfligersdorffer_at_[hidden])
Date: 2008-08-25 04:00:01

Hi Ákos,

I like your style of critics. Always put a reference to your opinion so it gets more weight. However I do not agree with everything you write. 

Ákos Maróy on Sunday, August 24, 2008 10:42 AM:

> Christian,
> 
>> And gcc-4, which also supports the #pragma once. The use of this
> 
> But the #pragma keyword is not for this. Even the MSDN page
> for #pragma
> says:
> 
> "Each implementation of C and C++ supports some features
> unique to its host machine or operating system ... The
> #pragma directives offer a way for each compiler to offer
> machine- and operating system-specific features"
> 
> see http://msdn.microsoft.com/en-us/library/d9x1s805(VS.80).aspx
> 
> having to guard a header file from inclusion is in no way a
> machine or OS dependent 'feature', thus it's not something
> you'd want to solve with #pragma.

I think in this point you're mistaken, since the pragma is simply a communication channel directly to your compiler. GCC offers not only machine or architecture pragmas but also e.g. diagnostic pragmas, the #pragma message or means to change optimization level per compilation unit.

> also see chapter 24 from C++ Coding Standards by Herb Sutter
> and Andrei Alexandrescu, titled "Always write internal
> #include guards. Never write external #include guards.",
> http://www.gotw.ca/publications/c++cs.htm

I agree! Buut that's out of question.

> basically using #pragma once is bad style.

I strongly disagree :) It's shorter, thus more elegant, does not induce myriads of names like the preprocessor guards and is even faster. GCC also saw that and de-deprecated it in versions 4.x.

>> I include enough boost headers which implicitly include version.hpp
>> and the like so I need not bother making this explicit.
> 
> see chapter 23 from C++ Coding Standards by Herb Sutter and
> Andrei Alexandrescu, titled "Make header files
> self-sufficient.". the fact that you include version.hpp
> frequently doesn't mean it shouldn't be explicit in this
> header file. if a header uses a feature, it should include
> the header for that feature.

You got a point here. It probably doesn't hurt and makes the whereabouts of the BOOST_VERSION macro evident in my case.

> if you're interested I can send you a version of your
> implementation I changed, along the following:
> 
> - added #ifdef guards / removed #pragma once
> - made the files self-sufficient
> - removed signed / unsigned comparision / conversion warnings from the
> save() functions of both iarchive and oarchive
> - solved portability issue with right-shifting signed values in the
> save() function of portable_binary_oarchive (right-shifting
> signed values is implementation dependent)
> 
> I'd be glad to send it the changed code over, if interested.

Sure! I'm curious how you changed my code, send it right over please! :) Especially the right-shifting issue caught my interest! Do you have examples where right shifting does not repeat the sign bit? Let me see how you solved it.

Regards,

-- 
Christian Pfligersdorffer
Software Engineering
http://www.eos.info