What might cause 'undefined symbol' for typeinfo when loading dynamic library built with C++11 enabled?

[Jonathan Wakely]

On Thu, 13 Dec 2018 at 16:01, David Aldrich
<david.aldrich.ntml@gmail.com> wrote:
>
> Thank you Jonathan for your reply.
>
> The class does indeed contain a virtual method, but that method is defined.
> So I don't think that is the problem.
>
> I've disabled the loading of the troublesome .so library file and now
> another library is refusing to load. I am wondering whether this new
> problem is related and so would like to ask you about it.  The error
> message now is:
>
> undefined symbol: _ZN8StarLibs7LinkSim2NR6NRDmrs18MAX_NUM_CDM_GROUPSE (
> StarLibs::LinkSim::NR::NRDmrs::MAX_NUM_CDM_GROUPS )
>
> This symbol is a constant defined in a class's header (.h file):
>
> namespace StarLibs {
> namespace LinkSim {
> namespace NR
> {
> class NRDmrs
> {
> public:
>
>         static const unsigned DMSR_MAX_NSCID = 1;
>         static const unsigned MAX_NUM_CDM_GROUPS = 3;
>
> This takes me back to my earlier comment.  In C++14, do I need to declare
> such constants in a .cpp source file in order to give them storage and so
> make them load?

If you use them in a way that requires an object with storage (e.g.
take their address or bind a reference to them) then yes. See
https://gcc.gnu.org/wiki/VerboseDiagnostics#missing_static_const_definition

Both your errors are linker errors due to missing symbols, but the
causes are entirely different. The only way they could have the same
cause is if you're forgetting to link to the file that contains those
symbols.