Re: [Boost-users] Using parse_config_file from program_options

Subject: Re: [Boost-users] Using parse_config_file from program_options
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-10-22 11:42:11

AMDG

Arthur Carlsson wrote:
> When I try to use the parse_config_file() function from the 
> program_options library I get a link error saying (built on OS X 10.5):
>
> Undefined symbols:
> "boost::program_options::basic_parsed_options<char> 
> boost::program_options::parse_config_file<char>(std::basic_istream<char, 
> std::char_traits<char> >&, boost::program_options::options_description 
> const&, bool)", referenced from:
> _main in main.cc.o
> ld: symbol(s) not found
>
> Taking a closer look at the code I discovered that the function is 
> declared as a template in boost/program_options/parsers.hpp but is 
> defined in boost/libs/program_options/src/parsers.cpp.
> Is this really valid? I've thought that templated functions need to be 
> defined along with the declaration as the template arguments need to 
> be evaluated at compile time.
> Or am I missing something?

It is legal to define templates in the source files as long as they are
explicitly instantiated, which is what these lines after the definition 
are for

    template
    BOOST_PROGRAM_OPTIONS_DECL basic_parsed_options<char>
    parse_config_file(std::basic_istream<char>& is,
                      const options_description& desc,
                      bool allow_unregistered);

As long as you are linking to the program_options library, it should be 
fine.

In Christ,
Steven Watanabe