[boost] Re: [program_options] cw9.3 failures

From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-09-25 05:08:27

Howard Hinnant wrote:

>> parsers.hpp contain:
>>
>>     template<class charT>
>>     basic_parsed_options<charT>
>>     parse_config_file(std::basic_istream<charT>&, const
>> options_description&);
>>
>> parsers.cpp contain:
......
>>     template
>>     BOOST_PROGRAM_OPTIONS_DECL basic_parsed_options<char>
>>     parse_config_file(std::basic_istream<char>& is,
>>                       const options_description& desc);
>>
>> And the linker can't find the explicitly instantinated function. This
>> happens
>> only in _dll tests, so I'd suspect a bug in the compiler/linker.
>>
>> Can anybody sched the light on this?
> 
> How are clients (who can view only parsers.hpp) to know that:
> 
> template<>
>      basic_parsed_options<char>
>      parse_config_file(std::basic_istream<char>& is,
>                        const options_description& desc);
> 
> is a function to be imported from a DLL?  

I don't know ;-) Somehow, msvc and borland don't care much.

> Does adding to parsers.hpp 
> something like:
> 
> template<> __declspec(dllimport)
>      basic_parsed_options<char>
>      parse_config_file(std::basic_istream<char>& is,
>                        const options_description& desc);
> 
> help?

I don't think I can do this. That's explicit specialization, and and I've be
required to provide the definition for it, and for wchar_t as well, no?

This means I'd have to provide two identical definitions for char and
wchar_t specializations? Or use an internal function that each
specialization will call? This does not sound right, I only want to
explicit instnantiate the function. And I think there's no way to "forward
declare" an explicit instantiation. What do you think?

In the meantime, I'll try adding declspec to the primary template
definition.

- Volodya