Re: [Boost-users] BOOST_STATIC_CONST

Subject: Re: [Boost-users] BOOST_STATIC_CONST
From: Olivier Tournaire (olitour_at_[hidden])
Date: 2010-03-13 03:43:18

Thank you Steven,

2010/3/13 Steven Watanabe <watanabesj_at_[hidden]>

> AMDG
>
>
> Olivier Tournaire wrote:
>
>> I am currently having problem with a static const class member (in a
>> header
>> only project):
>>
>> // type.hpp
>> template< typename Property >
>> struct property_base
>> {
>>    typedef Property type;
>> };
>>
>> struct some_type : property_base< uint32_t >
>> {
>>    BOOST_STATIC_CONSTANT( type, first_value       = 1 );
>>    BOOST_STATIC_CONSTANT( type, second_value  = 2 );
>> };
>>
>> // main.cpp
>> #include "type.hpp"
>> ...
>> int main(int argc, char** argv)
>> {
>>   BOOST_CHECK_EQUAL( 1     , some_type::first_value );
>> }
>>
>> This produces a link error (g++ 4.3.4): undefined reference to
>> some_type::first_value. Everything is fine with visual ...
>>
>> If I add const some_type::type some_type::first_value; after the struct
>> definition, it compiles and links fine. However, would it produce a
>> multiple
>> definition link error in some cases?
>> Could you please help?
>>
>>
>
> Putting the definition in a header can indeed cause a multiple
> definition error.  The definition needs to be in a cpp file.
>

Is there an other way to do that? I want the project to stay header only so
I cannot introduce a cpp file.
Are they some metaprogramming techniques that could lead to the same
behavior?

Regards,

Olivier

>
> In Christ,
> Steven Watanabe
>
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