function template methods and DLL exports

[Alfonso Morra]

I have a class declared as ff:

class __declspec(dlle xport) A {
public:
A() ;
A(const A&)
A& operator=(const A&) ;
~A() ;

void doThis(void) ;
void doThat(void) ;
template <class T> T doTheOther( const &T, int ) ;

private:
std::string s ;
std::vector< <std::pair> > vp ;
......
};
When I compile the code, the compiler generates several warnings such as:

warning C4251: 'A::s' : class 'std::basic_str ing<_Elem,_Trai ts,_Ax>'
needs to have dll-interface to be used by clients of class 'A'
with
[
_Elem=char,
_Traits=std::ch ar_traits<char> ,
_Ax=std::alloca tor<char>
]

etc. Why do I have to export private variables (is that what the warning
message is instructing me to do?)

Despite the warnings, the code builds and the dll is built. When I use
the dll in another project, problems (unsuprisingly) arise but they are
of a slightly different kind. The function template method doTheOther
does not seem to be exported and I am getting a link error when I try to
link to A.lib so I can create a project that uses classes exported by A.dll

I have two questions:

1). Why do I need to decorate the private variables with
__declspec(dlle xport) - as per compiler warnings?

2). Why is the method function template not getting exported (how do I
export the method in the DLL) ?
Thanks

[Nishant Sivakumar]

The answer to this and your previous post can both be obtained from this KB
article : http://support.microsoft.com/kb/q168958/

--
Regards,
Nish [VC++ MVP]
http://www.voidnish.com
http://blog.voidnish.com
"Alfonso Morra" <sw***********@ the-ring.com> wrote in message
news:db******** **@nwrdmz01.dmz .ncs.ea.ibs-infra.bt.com...

I have a class declared as ff:

class __declspec(dlle xport) A {
public:
A() ;
A(const A&)
A& operator=(const A&) ;
~A() ;

void doThis(void) ;
void doThat(void) ;
template <class T> T doTheOther( const &T, int ) ;

private:
std::string s ;
std::vector< <std::pair> > vp ;
......
};
When I compile the code, the compiler generates several warnings such as:

warning C4251: 'A::s' : class 'std::basic_str ing<_Elem,_Trai ts,_Ax>' needs
to have dll-interface to be used by clients of class 'A'
with
[
_Elem=char,
_Traits=std::ch ar_traits<char> ,
_Ax=std::alloca tor<char>
]

etc. Why do I have to export private variables (is that what the warning
message is instructing me to do?)

Despite the warnings, the code builds and the dll is built. When I use the
dll in another project, problems (unsuprisingly) arise but they are of a
slightly different kind. The function template method doTheOther does not
seem to be exported and I am getting a link error when I try to link to
A.lib so I can create a project that uses classes exported by A.dll

I have two questions:

1). Why do I need to decorate the private variables with
__declspec(dlle xport) - as per compiler warnings?

2). Why is the method function template not getting exported (how do I
export the method in the DLL) ?
Thanks

[Tamas Demjen]

Alfonso Morra wrote:

warning C4251: 'A::s' : class 'std::basic_str ing<_Elem,_Trai ts,_Ax>'
needs to have dll-interface to be used by clients of class 'A'
with
[
_Elem=char,
_Traits=std::ch ar_traits<char> ,
_Ax=std::alloca tor<char>
]
You may also want to read
http://www.unknownroad.com/rtfm/Visu...ningC4251.html
Although I didn't have a linker error problem related to exporting STL
classes. ("Workaround 2 can cause link errors..." doesn't seem to happen
to me). Be cautious, though. Also, the macros on this site don't work at
all. They may be for a very old version of VC++.

As an experiment, I worked out a small set of macros for exporting STL
containers, if you're interested. It's been tested with VC++ 2005 Beta 2
so far, but should also work with VC++ 2003. You definitely need to
modify it for different STL implementations . It's very compiler / STL
specific, thus the #if defined(_MSC_VE R).

#ifndef DllExportH
#define DllExportH

#if defined(_MSC_VE R)

#ifdef _DEBUG
# define class_it_base class
#else
# define class_it_base struct
#endif

#define EXPORT_STL_VECT OR(declspec_, T_) \
template class declspec_ std::allocator< T_ >; \
template class declspec_ std::vector<T_ >;

#define EXPORT_STL_VECT OR_CONST_ITERAT OR(declspec_, T_) \
class_it_base declspec_ std::_Iterator_ base; \
template class declspec_ std::_Vector_co nst_iterator<T_ ,\
std::allocator< T_ > >;

#define EXPORT_STL_DEQU E(declspec_, T_) \
template class declspec_ std::allocator< T_ >; \
template class declspec_ std::allocator< T_* >; \
template class declspec_ std::deque<T_ >;

#define EXPORT_STL_LIST (declspec_, T_) \
template class declspec_ std::allocator< T_ >; \
template class declspec_ std::allocator< std::_List_nod< T_,\
std::allocator< T_ > >::_Node>; \
template class declspec_ std::allocator< std::_List_nod< T_,\
std::allocator< T_ > >::_Node*>; \
template class declspec_ std::list<T_ >;

#define EXPORT_STL_SET( declspec_, T_) \
template class declspec_ std::allocator< T_ >; \
template struct declspec_ std::less<T_ >; \
template class declspec_ std::allocator< std::_Tree_nod< \
std::_Tset_trai ts<T_, std::less<T_ >, std::allocator< T_ >, false> \::_Node>; \ template class declspec_ std::allocator< std::_Tree_ptr< \
std::_Tset_trai ts<T_, std::less<T_ >, std::allocator< T_ >, false> \::_Node*>; \ template class declspec_ std::set<T_ >;

#define EXPORT_STL_MULT ISET(declspec_, T_) \
template class declspec_ std::allocator< T_ >; \
template struct declspec_ std::less<T_ >; \
template class declspec_ std::allocator< std::_Tree_nod< \
std::_Tset_trai ts<T_, std::less<T_ >, std::allocator< T_ >, true> \::_Node>; \ template class declspec_ std::allocator< std::_Tree_ptr< \
std::_Tset_trai ts<T_, std::less<T_ >, std::allocator< T_ >, true> \::_Node*>; \ template class declspec_ std::multiset<T _ >;

#define EXPORT_STL_MAP( declspec_, K_, V_) \
template struct declspec_ std::less<K_ >; \
template class declspec_ std::allocator< std::_Tree_nod< \
std::_Tmap_trai ts<K_, V_, std::less<K_ >, \
std::allocator< std::pair<const K_, V_ > >, false> >::_Node>; \
template class declspec_ std::allocator< std::_Tree_nod< \
std::_Tmap_trai ts<K_, V_, std::less<K_ >, \
std::allocator< std::pair<const K_, V_ > >, false> >::_Node*>; \
template class declspec_ std::allocator< std::pair<const K_, V_ > >; \
template class declspec_ std::map<K_, V_ >;

#define EXPORT_STL_MAP_ CONST_ITERATOR( declspec_, K_, V_) \
class_it_base declspec_ std::_Iterator_ base; \
template class declspec_ std::_Tree<std: :_Tmap_traits<K _, V_, \
std::less<K_>, std::allocator< std::pair<const K_, V_ > >, false> \::const_iterat or;

#define EXPORT_STL_MULT IMAP(declspec_, K_, V_) \
template struct declspec_ std::less<K_ >; \
template class declspec_ std::allocator< std::_Tree_nod< \
std::_Tmap_trai ts<K_, V_, std::less<K_ >, \
std::allocator< std::pair<const K_, V_ > >, true> >::_Node>; \
template class declspec_ std::allocator< std::_Tree_nod< \
std::_Tmap_trai ts<K_, V_, std::less<K_ >, \
std::allocator< std::pair<const K_, V_ > >, true> >::_Node*>; \
template class declspec_ std::allocator< std::pair<const K_, V_ > >; \
template class declspec_ std::multimap<K _, V_ >;

#else

#define EXPORT_STL_VECT OR(declspec_, T_)
#define EXPORT_STL_VECT OR_CONST_ITERAT OR(declspec_, T_)
#define EXPORT_STL_DEQU E(declspec_, T_)
#define EXPORT_STL_LIST (declspec_, T_)
#define EXPORT_STL_SET( declspec_, T_)
#define EXPORT_STL_MULT ISET(declspec_, T_)
#define EXPORT_STL_MAP( declspec_, K_, V_)
#define EXPORT_STL_MAP_ CONST_ITERATOR( declspec_, K_, V_)
#define EXPORT_STL_MULT IMAP(declspec_, K_, V_)

#endif

#endif