Global and file-static variables in static library

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In some code I wrote for a client, I use the "self-registering plugin pattern:

// D1.h

class D1: public Base
{
public:
D1();
// declare virtual overrides
};

//--------------------------------------------------

// D1.cpp

#include "D1.h"

namespace
{
Base* Create(){return new D1;}
bool auto_register = RegisterPlugin("D1", Create);
}

D1::D1(){}
// virtual function definitions for D1

//--------------------------------------------------

The function RegisterPlugin() creates an entry in a map of strings to function pointers, which allows a factory function to create an instance of the plugin D1 from its name "D1". The key feature of the pattern is that the file D1.h is not #include'd anywhere except D1.cpp. It works despite the fact that the code in D1.cpp is superficially not used by the rest of the program. It works on VC7.1 and VC8 and various unix/linux compilers.

Recently, however, using VC8, the client got it into his head to compile my code into a static library (.lib) before linking it to his code. And now the pattern does not work any more (the map is not populated).

Initially I thought this might be because I placed the code in an anonymous namespace ("file-static"), but the same thing happens if I make auto_register a global variable (using a different name for each plugin).

It seems that when a .obj file is embedded in a static library, and then linked with a client program such that the content of that .obj is apparently unused, the content of that .obj file is not contained in the image. This does not happen if the .obj files are linked individually.

Why does this happen? And what should I do about it? [I have found a couple of workarounds, but they require explicit reference to something in the plugin implementation, which rather spoils the beauty of the pattern.]

--
David Wilkinson
Visual C++ MVP
.

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