RE: [GD-Windows] dll export and template

[Nicolas R. <nic...@fr...>]

Yes... template and DLLs are badly working together...

Under VC7 you can at least declare the template exported...
template<class T> class __declspec(dllexport) mytemplate
{
};
will correctly export the template.


Note however that the export is only done on used template definitions... Export/import
scheme defined automatically by VC++ is not sufficient...
Let say you have a header containing:
template<class T> class MYDLL_API mytemplate
{
};

A DLL is compiling with MYDLL_API to __declspec(dllexport). If it use it with T =
MyDLLClass1 and MyDLLClass2, only mytemplate<DLLClass1> and mytemplate<DLLClass2> will be
exported.

If an external program is including the header (with MYDLL_API to __declspec(dllimport))
it won't be able to use the template for a "ExeClass" since it won't be exported by any
DLL...


Still havent find any way to correctly export the template itself (but using the #pragma
warning(disable:xxxx) before using a non exported template).


Nicolas.




-----Original Message-----
From: gam...@li...
[mailto:gam...@li...]On Behalf Of
jason zhang
Sent: lundi 5 août 2002 09:48
To: gam...@li...
Subject: [GD-Windows] dll export and template


There was a compile warning when I  use template in my export class of DLL.  And the
compiler
will give an error if I put __declspec(dllexport) keyword before the my template
definition.
My question is whether it is safe if I just disable the warning.

The warning is:
"The specified base class was not declared with the __declspec(dllexport) keyword.A base
class or structure must be declared with the __declspec(dllexport) keyword if a function
in a derived class is to be exported. "
.
The code is:
template<class T> mytemplate
{
    T t;
public:
    void SetData( T &_t ){ t = _t; }
};

class MYDLL_API MyClass
{
    mytemplate<int> data;

public:
    ....
};


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