__declspec(dllexport)

You can use __declspec(dllexport) on a function, a class, or on individual members of a class.

When an inline function is marked __declspec(dllexport), the function definition might be inlined, but an out-of-line instance of the function is always generated and exported in the same way as for a non-inline function.

When a class is marked __declspec(dllexport), for example, class __declspec(dllexport) S { ... }; its static data members and member functions are all exported. When individual static data members and member functions are marked with __declspec(dllexport), only those members are exported. vtables, construction vtable tables and RTTI are also exported.

class __declspec(dllexport) S { ... };

__declspec(dllexport) class S { ... };

In conjunction with --export_all_vtbl, you can use __declspec(notshared) to exempt a class or structure from having its vtable, construction vtable table and RTTI exported. --export_all_vtbl and __declspec(dllexport) are typically not used together.

If you mark a class with __declspec(dllexport), you cannot then mark individual members of that class with __declspec(dllexport).

If you mark a class with __declspec(dllexport), ensure that all of the base classes of that class are marked __declspec(dllexport).

If you export a virtual function within a class, ensure that you either export all of the virtual functions in that class, or that you define them inline so that they are visible to the client.

The __declspec() required in a declaration depends on whether or not the definition is in the same shared library.

/* This is the declaration for use in the same shared library as the */
/* definition */
__declspec(dllexport) extern int mymod_get_version(void);

/* Translation unit containing the definition */
__declspec(dllexport) extern int mymod_get_version(void)
{
   return 42;
}

/* This is the declaration for use in a shared library that does not contain */
/* the definition */
__declspec(dllimport) extern int mymod_get_version(void);

As a result of the following macro, a translation unit that does not have the definition in a defining link unit sees __declspec(dllexport).

/* mymod.h - interface to my module */
#ifdef BUILDING_MYMOD
#define MYMOD_API __declspec(dllexport)
#else /* not BUILDING_MYMOD */
#define MYMOD_API __declspec(dllimport)
#endif

MYMOD_API int mymod_get_version(void);