C++: How to create a DLL and calling it from application?

I create the DLL first,

Main.h

#ifndef __MAIN_H__

#define __MAIN_H__

#include <windows.h>

/* To use this exported function of dll, include this header

* in your project.

*/

#ifdef BUILD_DLL

#define DLL_EXPORT __declspec(dllexport)

#else

#define DLL_EXPORT __declspec(dllimport)

#endif

 

#ifdef __cplusplus

extern "C"

{

#endif

void DLL_EXPORT SomeFunction(const LPCSTR sometext);

#ifdef __cplusplus

}

#endif

#endif // __MAIN_H__

 

Main.cpp

#include "main.h"

// a sample exported function

void DLL_EXPORT SomeFunction(const LPCSTR sometext)

{

MessageBoxA(0, sometext, "DLL Message", MB_OK | MB_ICONINFORMATION);

}

BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved)

{

switch (fdwReason)

{

case DLL_PROCESS_ATTACH:

// attach to process

// return FALSE to fail DLL load

break;

case DLL_PROCESS_DETACH:

// detach from process

break;

case DLL_THREAD_ATTACH:

// attach to thread

break;

case DLL_THREAD_DETACH:

// detach from thread

break;

}

return TRUE; // succesful

}

 

Build the DLL then create the application to call the function. You must put the correct DLL path.

 

#include <iostream>

#include <windows.h>

using namespace std;

// pointer to function in dll, caller of CallDll

typedef __declspec(dllimport)DWORD(*pfFunc)(const LPCSTR sometext);

int main()

{

HINSTANCE hDll = ::LoadLibrary("D:\\ bin\\Debug\\araoarao.dll"); // put your own DLL path here

pfFunc pFun = NULL;

pFun = (pfFunc)::GetProcAddress(hDll, "SomeFunction");

pFun("Hello World!!");

return 0;

}

 

After successful linking when you run the application it will display a message box with "Hello World"

 

Thant's it!