Thank you Steven, 2010/3/13 Steven Watanabe

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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On Sat, 13 Mar 2010 09:43:18 +0100 Olivier Tournaire wrote:

Thank you Steven,

2010/3/13 Steven Watanabe

...

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?

Is "extern" what you are looking for? extern const some_type::type some_type::first_value; Cheers, -- Manfred

On Sat, 13 Mar 2010 19:58:00 +0100 Olivier Tournaire wrote:

2010/3/13 Manfred Doudar

...

On Sat, 13 Mar 2010 09:43:18 +0100 Olivier Tournaire wrote:

...

Thank you Steven,

2010/3/13 Steven Watanabe

...

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?

Is "extern" what you are looking for?

Maybe. However, I am not sure. I still have to provide a definition of the member somewhere. Where should I do this (in a header only project ...)?

...

extern const some_type::type some_type::first_value;

If you add the line above (extern ...) just after your struct some_type in type.h, works for me. Cheers, -- Manfred