C / C++ / MFC

// foo.h

#ifdef _DLLPROJ_
#define DLLEXP __declspec (dllexport)
#else 
#define DLLEXP __declspec (dllimport)
#endif

DLLEXP class CFoo
{
public:

	DLLEXP int foo1();

	DLLEXP int foo2();
};

DLLEXP class CFooImpl : CFoo
{
public:

	DLLEXP CFooImpl();

	DLLEXP int foo1();

	DLLEXP int foo2();
};

// dllmain.cpp

#include "foo.h"

CFooImpl::CFooImpl()
{
	return;
}

int CFooImpl::foo1()
{
	return 100;
}

int CFooImpl::foo2()
{
	return 200;
}

DLLEXP CFooImpl foo;

// main.cpp

#include "foo.h"

DLLEXP CFooImpl foo;

int main()
{
	CFooImpl foo1;

	int i = foo.foo1();
	i = foo.foo2();

	return 0;
}

George_George wrote:

DLLEXP class CFoo

#if!defined(COMMONLIB_API)
#ifdef COMMONLIB_EXPORTS
#define COMMONLIB_API __declspec(dllexport)
#else
#define COMMONLIB_API __declspec(dllimport)
#endif
#endif

namespace MyAppLibrary {

   class MessageReporter {

      public:

         //ctor
         COMMONLIB_API MessageReporter();

         //Add new reporting function
         COMMONLIB_API static void AddReportFunction(ReportFnPtr func);

         //Set MessageReporter Level on or off
         COMMONLIB_API static void SetReporterLevel(Level lev, bool on);

         //Set all levels to on
         COMMONLIB_API static void AllLevelsOn() {repLevels=~0;}

         //Set all levels to off
         COMMONLIB_API static void AllLevelsOff() {repLevels=0;}
   };
};

a.h

#if !defined(__A_H__)
#define __A_H__

#if!defined(A_API)
#ifdef A_EXPORTS
#define A_API __declspec(dllexport)
#else
#define A_API __declspec(dllimport)
#endif
#endif

class A_API A
{
public:
    A();
    A(int a);
    void DoSomething(int b);
    int Result() const;
private:
    int a_;
};

#endif // !defined(__A_H__)

a.cpp

#include <windows.h>
#define A_EXPORTS
#include "a.h"

BOOL APIENTRY DllMain( HANDLE hModule, 
                       DWORD  ul_reason_for_call, 
                       LPVOID lpReserved
					 )
{
    return TRUE;
}

A::A() : a_(0) {}
A::A(int a) : a_(a) {}
void A::DoSomething(int b) { a_ += b; }
int A::Result() const { return a_; }

b.cpp

#include <iostream>
#include "a.h"

int main(int argc, char** argv)
{
    A a(argc);
    
    a.DoSomething(3);
    std::cout << a.Result() << std::endl;
}

1. In main.cpp, you want to declare CFoo as __declspec(dllimport). The way I do that is to put something like this in foo.h:
   
   

   #if !defined(FOO_DLL)
   #define FOO_EXP __declspec(dllimport)
   #else
   #define FOO_EXP __declspec(dllexport)
   #endif
   
   class FOO_EXP CFoo { ... };

   
   
   You would define FOO_DLL when building the DLL using, for example, #define FOO_DLL in every source file in the DLL before #including foo.h. You need do nothing in main.cpp>/code>, as that's what the default case caters for.
2. As other replies have said, you would need to export CFoo foo; from the DLL.

manish rastogi wrote:

I am writing an utility dll like dependency walker. I have no idea how to get dependent dll.

rukawa84 wrote:

wchar_t* seems more convenient, but I'm actually linking these to other DLL files, and the only input type to those is const char*, this I can't change. You have any idea about this conversion code?