C / C++ / MFC

#ifdef BF_EXPORTS
#define BF_API __declspec(dllexport)
#else
#define BF_API __declspec(dllimport)
#endif

// This class is exported from the BF.dll
class BF_API CBar {
      public:
          CBar( void ) {
              m_bFlag = true;
            }
      private: 
          bool m_bFlag;
  };


class BF_API CFoo {
      public:
          CFoo( void ) {
            }

          CBar * MakeBar( void ) {
              CBar * cResult = new CBar();
              return cResult;
            }
  };

#include <stdio.h>
#include "BF.h"

int main(int argc, char* argv[])
  {
    CFoo * foo = new CFoo;
    CBar * bar = foo->MakeBar();

    delete bar;
    delete foo;

    return 0;
  }

• Passing buffered stream handles from the .EXE/DLL to the other module
  
• Allocating memory with a C Run-time call in the .EXE/DLL and
  reallocating or freeing it in the other module
  
• Checking or setting the value of the global errno variable in the
  .EXE/DLL and expecting it to be the same in the other module. A related
  problem is calling perror() in the opposite module from where the C Run-
  time error occurred, since perror() uses errno.