Dear Jim,

I remember having some troubles using boost::optional with boost::program_options.
I fixed it by adding the following lines:

namespace boost
{
// Add custom validator to use boost::program_options on boost::optional<> types
template<class T>
void validate(boost::any& v, std::vector<std::string> const& values, boost::optional<T>* typeTag, int)
{
    if (!values.empty())
    {
        boost::any a;
        using namespace boost::program_options;
        validate(a, values, (T*)0, 0);
        v = boost::any(boost::optional<T>(boost::any_cast<T>(a)));
    }
}
}

I don’t remember the details, but I think I took that from more recent version of Boost to be able to use my code with older version of Boost.
With that, my code compiles and runs fine

• on Linux for Boost from 1.54 to 1.66 with various compilers (GCC 4.8 to 7.3, Intel Compiler, Clang)
• on Windows for Boost 1.60 with MSVC++ from 9 (2008) to 14 (2015).

I hope this will help.

Best regards,

Xavier