C++ Plugins and virtual destructors.

[Brendon Costa]

Hi all,

Is using virtual destructors fine with a C++ plugin interface?

I have an example below that works. However i am not sure if it is a
good practice. In particular is it ok to make use of virtual
destructors in an application to destroy an object allocated in the
plugin or should I define a pure virtual Destroy() method to ensure
that the actual memory de-allocation (call to delete) is performed in
the plugin where it was also initially allocated?

Thanks,
Brendon.




Compile below using:
g++ -o main -Wall -g -fPIC main.cpp -lltdl
g++ -o myplugin.so -shared -Wall -g -fPIC myimpl.cpp


---- myiface.h ----
class MyIFace
{
public:
   virtual ~MyIFace() {}
   virtual void DoStuff() = 0;
};

---- myimpl.cpp ----
#include "myiface.h"
#include <iostream>

namespace
{
   class MyImpl : public MyIFace
   {
   public:
      MyImpl() :
         blah("Hello")
      {}

      virtual void DoStuff()
      {
         std::cout << "DoStuff: " << blah << std::endl;
      }

   private:
      std::string blah;
   };
}

// For GCC on UNIX
#define MY_CALLTYPE __attribute__((cdecl))
#define MY_EXPORT __attribute__ ((visibility("default")))

extern "C"
{
   MY_EXPORT void* MY_CALLTYPE MyFactory(void)
   {
      return static_cast<void*>(new MyImpl());
   }
}


---- main.cpp ----
#include "myiface.h"
#include <iostream>
#include <ltdl.h>

typedef void* (*CreateFP)(void);

int main()
{
   lt_dlinit();
   lt_dladdsearchdir(".");
   lt_dlhandle module = lt_dlopenext("myplugin");
   CreateFP create_fp  = (CreateFP)lt_dlsym(module, "MyFactory");
   MyIFace* iface = static_cast<MyIFace*>(create_fp());
   iface->DoStuff();

   // Delete the instance!!!!!!!!!!!
   // IS THIS A GOOD IDEA?
   delete iface;
   iface = NULL;

   lt_dlclose(module);
   lt_dlexit();
   return 0;
}