Re: unresolved external symbol with static variable?

From:

"JSprenkle@gmail.com" <JSprenkle@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Sat, 31 Mar 2007 14:31:02 CST

Message-ID:

<1175358867.920241.122810@o5g2000hsb.googlegroups.com>

On Mar 31, 10:30 am, cbarr...@ix.netcom.com (Carl Barron) wrote:

JSpren...@gmail.com <JSpren...@gmail.com> wrote:

  In the faq the authors says:
  "The map is typically populated during static initialization. For
  example, if file Ellipse.cpp contains the code for derived class
  Ellipse, it would also contain a static object whose ctor adds that
  class to the map: theMap["Ellipse"] = new Ellipse()."

  What is he trying to say here?

  Any help would be appreciated.

   I think he is saying create:
    // Ellipsis.cp
    #include "Ellispsis.hpp"
    #include "Serialize.hpp" // for extern std::map<...> theMap;

    namespace
    {
        struct add_to_map
        {
              add_to_map()
              {
                  theMap["Ellipsis"] = new Ellipsis();
              }
        };
        add_to_map foo;
   }
   // impliment ellipsis don't use foo anyplace in this file
   // end of file

At least that is a literal translation.

Thanks :)

I found most of my problem was not understanding that static's are
really globals without
global scope. You have to actually instantiate them in one of your
source files. if you don't
then you get the 'unresolved external' error. The tricky bit here
turned out to be since maps
use [] you can't just initialize them with map[5] = "foo"; The
compiler thinks you're declaring
an array and gives errors. If you do a static class and initialize it
in that class then it
works. Or at least it compiles... ;)

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