Re: [!! RANT !!] This is a hack at best (C4251)
- From: "Nishant Sivakumar" <nish@xxxxxxxxxxxxxxxxxxxxxxx>
- Date: Mon, 25 Jul 2005 09:13:04 +0530
The template function won't be generated until it's instantiated. So, you
really cannot export template functions from a DLL. The right way to use
templates is via a header file.
Or you could use the below technique (quite ugly I might add) :-
e.g. :-
template<typename T> void foo(T t) {...}
//export the below functions
void fooint(int t)
{
foo<int>(t);
}
void foochar(char t)
{
foo<char>(t);
}
void fooCWnd(CWnd t)
{
foo<CWnd>(t);
}
etc . . .
Export functions for every possible template specialization that the calling
code might need.
But again, the right way to do this is to include the header file defining
the template function in your calling project.
--
Regards,
Nish [VC++ MVP]
http://www.voidnish.com
http://blog.voidnish.com
"Alfonso Morra" <sweet-science@xxxxxxxxxxxx> wrote in message
news:dc0bdk$3ai$1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
>
> Peter van der Goes wrote:
>
>> "Alfonso Morra" <sweet-science@xxxxxxxxxxxx> wrote in message
>> news:dbt5jp$l9h$1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>
>>>I cannot believe how convoluted it is to export function templates and
>>>class templates from a shared library (or DLL as it is called in the
>>>Windoze world).
>>>
>>>Micro$oft support for STL and standards in general is absolutely
>>>appaling. This is absolutely ridiculous. I have obtaind links from people
>>>who tried to help me solve this problem, several days ago, to no avail.
>>>Even the sample code at http://support.microsoft.com/kb/q168958/ when
>>>adapted to my code (i.e. #defines specified etc), still generates
>>>compiler errors like:
>>>
>>>error C2757: 'std' : a symbol with this name already exists and therefore
>>>this name cannot be used as a namespace name
>>>
>>>This is from code provided by Microsoft. I TRULY HATE Microsoft (there I
>>>said it), and their non-standard, proprietary way of doing everything. I
>>>would not touch their flaky compilers if I did not have to work with them
>>>...Arghhhh, I'm going out for a cofee break !
>>>
>>
>> Perhaps when you return from your break, you'll provide some amplifying
>> information about the problem you are having? That might make it possible
>> for someone here to help you.
>>
>
> Hi peter,
>
> Thanks for offering to help. This is really driving me round the bend. I
> have a little sample code below, which compiles and builds (with
> warnings). The built DLL exports the symbols, so I am not sure why the
> compiler issues the warnings (however, I have not tried to use the built
> DLL).
>
> Here is the code:
>
>
> using std::string ;
> using std::vector ;
>
> #ifdef TESTDLL_EXPORTS
> #define CCONV __declspec(dllexport)
> #else
> #define CCONV __declspec(dllimport)
> #endif
>
> class CCONV MyClass {
> public :
> MyClass():m_name("test"),val(0){} ;
> ~MyClass(){} ;
>
> inline string getName( void ){ return m_name ; }
> inline void setName( string new_name ) { this->m_name = new_name ; }
>
> template <class T1, class T2>
> void foo( T1 arg1, T2 arg2 ) {
> ;//dummy
> };
>
> inline vector<int> getDates( void ){ return dates ; }
>
> private:
> //prevent copy and assignment
> MyClass( const MyClass& ) ;
> MyClass& operator=(const MyClass&) ;
>
> /* Nested class */
> class MyNestEgg {
> friend class MyClass ;
> void doThis(void){;}
> void doThat(void){;}
> };
>
> string m_name ;
> int val ;
> MyNestEgg m_nuts ;
> vector<int> dates ;
>
> public:
> inline void doThisToMyNestEgg( void ) { m_nuts.doThis() ; }
> inline void doThatToMyNestEgg( void ) { m_nuts.doThis() ; }
>
> };
>
>
>
> Two thing I must mentioned however, are:
>
> 1). I notice that the compiler does not complain about the myNestEgg
> variable. In my actual code, the compile complains as ff:
> "warning C4251: 'A::m_props' : class 'A::Properties' needs to have
> dll-interface to be used by clients of class 'A'
>
> 2). The function template is completely ignored and not even exported.
> This is not too suprising since it may require template specialiazation -
> but this is only a guess, siince I cannot find anything useful on
> Microsoft's site - and the code given there to allow exporting STL objects
> from a shlib does not work.
>
>
> I hope you can provide a fix as to how to get this to work (i.e. compile
> without warnings and to export STL classes). The actual code I have
> inherits from a template class like this:
>
> MyClass: public Singleton<MyClass> { ...}
>
> For now, i want to keep things simple, and I will discuss that once I have
> managed to get the simple class (i.e. with no inheritance extensions) to
> compile and export symbols correctly.
>
> MTIA
>
.
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- From: Nishant Sivakumar
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- [!! RANT !!] This is a hack at best (C4251)
- From: Alfonso Morra
- Re: [!! RANT !!] This is a hack at best (C4251)
- From: Peter van der Goes
- Re: [!! RANT !!] This is a hack at best (C4251)
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