Re: [boost] Detection of 64bit using macro

Subject: Re: [boost] Detection of 64bit using macro
From: Jeffrey Lee Hellrung, Jr. (jhellrung_at_[hidden])
Date: 2010-08-13 16:13:42

On 8/13/2010 12:44 PM, Kim Kuen Tang wrote:
>
> Hi all,
>
> the question might be not directly related to boost. But i just want to
> be sure that i am not reventing the wheel.
> I am searching for a macro that is able to detect that a system is 32bit
> or 64bit no matter what compiler is used.
> Is there something similar already implemented in boost?
>
> Perhaps some background about this feature.
>
> Template specialization for std::size_t is not needed, when the
> specialization already exists for unsigned int. But on a 64bit system
> this is not true.
> So you need explicitly added the specialization whenever a 64bit
> compiler is used.
>
> See the following example.
>
> # include <cstddef>
>
> template<typename T>
> struct Null;
>
> template<> struct Null<unsigned int> {};
> template<> struct Null<std::size_t> {}; // compile only on a 64bit compiler
>
> int main()
> {
> return 0;
> };
>
> Thx for any comments, help or suggestions
>
> Kim

Perhaps you should just specialize on std::size_t conditional on it 
being different from an unsigned int, rather than on 64bit-ness:

template< class T, bool = boost::is_same< T, unsigned int >::value >
struct Null2;

template<>
struct Null2< unsigned int, true > { ... };
template<>
struct Null2< std::size_t, false > { ... };

template< class T >
struct Null : Null2<T> { };

There might be a "cleaner" way to achieve the same effect, but does that 
help?

- Jeff