shared_ptr, interface and dlls
Hi, is it possible to return a shared_ptr to an interface from a dl?. I thought of the following what unfortunately doesn't work: // Interface.h - exe project class Interface { public: vitrtual void f( void ) = 0; virtual void g( void ) = 0; protected: ~Interface( void ) {} } typedef shared_ptr<Interface> InterfacePtr; InterfacePtr Create( void ) { // Load a special create function from the dll //.... return DLLCreate(); } // InterfaceImpl.h - dll project #include Interface class InterfaceImpl : public Interface { public: void f( void ) { /* ... */ }; void g( void ) { /* ... */ }; private: // No copy operations } extern "C" InterfacePtr DLLCreate( void ) { return InterfacePtr( new InterfaceImpl ); } At the moment this code doesn't compile because VS7.1 complains that it a function with extern "C" linkage can't return a shared_ptr<Interface> instance. How could I implement the desired behavior? Some other related questions regarding this topic: 1.) I link to the multithreaded C run-time dll - is this allowed? I read in an older post that only static CRT linking is allowed. 2.) Does the above code - loading the factory from the DLL as well and (hopefully) constructing the instance there - solve the boundary problems? I read some articles regarding this issue, but to be honest I haven't completly understood the problems that may occure in this case so far. Any help is greatly appreiciated.. -Dirk
Dirk Gregorius wrote:
Hi,
is it possible to return a shared_ptr to an interface from a dl?. I thought of the following what unfortunately doesn't work:
[...]
extern "C" InterfacePtr DLLCreate( void ) { return InterfacePtr( new InterfaceImpl ); }
At the moment this code doesn't compile because VS7.1 complains that it a function with extern "C" linkage can't return a shared_ptr<Interface> instance. How could I implement the desired behavior?
Either omit the extern "C" or, if you must use a C-style interface, do this: extern "C" Interface* DLLCreate() { return new InterfaceImpl; } extern "C" void DLLDestroy( Interface* p ) { delete p; } and then construct an InterfacePtr( DLLCreate(), DLLDestroy ). You'll need a public virtual destructor in this case, though.
Some other related questions regarding this topic:
1.) I link to the multithreaded C run-time dll - is this allowed? I read in an older post that only static CRT linking is allowed.
Yes, it's allowed. Since you are using the DLL runtime, you probably don't need to interoperate with different C++ compilers so you probably need to just omit the extern "C" from DLLCreate.
2.) Does the above code - loading the factory from the DLL as well and (hopefully) constructing the instance there - solve the boundary problems? I read some articles regarding this issue, but to be honest I haven't completly understood the problems that may occure in this case so far.
Yes, it will work, as long as you don't unload the DLL that created the object before destroying the object first (using FreeLibrary).
participants (2)
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Dirk Gregorius -
Peter Dimov