Re: dll export question / stl problem / C4251

From:

"Tom Widmer [VC++ MVP]" <tom_usenet@hotmail.com>

Newsgroups:

microsoft.public.vc.stl

Date:

Tue, 12 Sep 2006 09:54:54 +0100

Message-ID:

<eVjCfkk1GHA.1336@TK2MSFTNGP03.phx.gbl>

scott mcfadden wrote:

When I mark a class that uses STL strings for export in a DLL project, VS
2003 gives me lots of warnings on my STL string class members:

#include <string>
using namespace std

class __declspec(dllexport) MyClass{
public:
//default constructor
MyClass();

//destructor
~MyClass();

  void DoIt();

  string getSource();

  bool setSource(string & source);

protected:

string m_source;
};

warning C4251: MyClass::source: class 'std::basic_string<_Elem,_Traits,_Ax>'
needs to have dll-interface to be used by clients of class MyClass

What causes these warnings? How can I avoid them?

In addition to the other replies, I think you can get rid of the error
by linking to the DLL version of the CRT (under settings->Code
generation->C/C++). That way, anything using your DLL can also link to
that version of the CRT, and therefore be using the same version of
std::string (which is obviously essential).

Note that this only works for std::string, not for other containers,
since std::string is exported from the DLL CRT.

Tom