Solved

dll-exporting a class defined with a template

Posted on 1998-09-13
3
230 Views
Last Modified: 2010-04-02
Hi,
The following code attempts to dll-export the class cBig; the MicroSoft Visual C++ 5.0 compiler generates the following warning:

warning C4251: 'mRange' : class 'TRange<long>' needs to have dll-interface to be used by clients of class 'CBig'

the code :
// Start of code
#define DllExport __declspec( dllexport )

template<class T> class TRange
{
.
.
}

class DllExport cBig
{
public:
.
.
protected:
    typedef TRange<long> CRange;
    CRange mRange;
}
// End of code

What should I do in order to resolve this warning? I've tried to insert an additional 'DllExport' almost everywhere in the code.
0
Comment
Question by:gil_mo
3 Comments
 
LVL 22

Expert Comment

by:nietod
ID: 1172584
I declared the template class as DllExport and added ";" to the ends of the classes like

template<class T> class DllExport TRange
   {
   } ;

   class DllExport cBig
   {
   public:
   protected:
       typedef TRange<long> CRange;
       CRange mRange;
   } ;

and it worked fine.
0
 

Author Comment

by:gil_mo
ID: 1172585
nietod,
warning persists if the class template isn't empty, e.g.

template<class T> class DllExport TRange
{
private:
    long a;
};

0
 
LVL 3

Accepted Solution

by:
xyu earned 50 total points
ID: 1172586
try to add this line before declaration of cBig

.
template class __declspec(dllexport) TRange<long>;
.
or
template<> class __declspec(dllexport) TRange<long>;

 it will help if TRange doesn't have outline implementation of the member functions like
template <class T> void TRange<T>::Foo() {...}

otherwise You'll receive on such a function warning like that..
"..dllexport assumed by default.." but its Ok... and You can live with it :) without any problem...

0

Featured Post

PRTG Network Monitor: Intuitive Network Monitoring

Network Monitoring is essential to ensure that computer systems and network devices are running. Use PRTG to monitor LANs, servers, websites, applications and devices, bandwidth, virtual environments, remote systems, IoT, and many more. PRTG is easy to set up & use.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Unlike C#, C++ doesn't have native support for sealing classes (so they cannot be sub-classed). At the cost of a virtual base class pointer it is possible to implement a pseudo sealing mechanism The trick is to virtually inherit from a base class…
In days of old, returning something by value from a function in C++ was necessarily avoided because it would, invariably, involve one or even two copies of the object being created and potentially costly calls to a copy-constructor and destructor. A…
The goal of the tutorial is to teach the user how to use functions in C++. The video will cover how to define functions, how to call functions and how to create functions prototypes. Microsoft Visual C++ 2010 Express will be used as a text editor an…
The viewer will learn how to pass data into a function in C++. This is one step further in using functions. Instead of only printing text onto the console, the function will be able to perform calculations with argumentents given by the user.

778 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question