Calling DLL with wrapper from Application exe

1. Create a MFC Appwizard(exe) the project name "TestDLL"
2. Using the wizard select dialog based application.
3. Add three "Edit Box" and add member name as m_edA, m_edB and m_edResult and choose Category as variable and Type as int.
   
4. Add a new class with class name "CWrapper" with class type "Generic Class".
5. Add a new header file with name "MyAPI.H".
   
6. Edit the following files as the instruction given below.
7. copy the "MyDll.dll" DLL created earlier and paste it where your exe application created. By default in "Debug" folder of your Project.
   

// Add the following lines in MyAPI.H
#define DLLNAME "MyDLL.dll"
//function pointers for Exportable API's
typedef int (*egAddFn) (int A, int B);


// Add the following lines in TestDLLDlg.h
#include "Wrapper.h"
class CTestDLLDlg : public CDialog
{
private:
CWrapper m_Wrapper; //add this line
};


//Add the following lines in Wrapper.h
#include "MyAPI.h"
class CWrapper
{
public:
OnInitialize(); //add this line
OnUnInitialize(); //add this line
HINSTANCE m_hInstance; //add this line
int egAdd(int a,int b); //add this line
egAddFn m_egAddFn; //add this line
};


//Add the following lines in TestDLLDlg.cpp
void CTestDLLDlg::OnBtnAdd()
{
UpdateData(TRUE);
int a=0,b=0,c=0;
a=m_edA; //name of the edit box with type int
b=m_edB; //name of the edit box with type int
if(m_Wrapper.m_egAddFn)
{
c=m_Wrapper.m_egAddFn(a,b);
}
m_edResult=c; //name of the edit box with type int
UpdateData(FALSE);
}


//Add the following lines in Wrapper.cpp:
#include "Wrapper.h"
CWrapper::CWrapper()
{
m_hInstance = NULL;
//Initialize all function pointers to NULL
m_egAddFn = NULL;
OnInitialize();
}

CWrapper::~CWrapper()
{
OnUnInitialize();
}

int CWrapper::OnInitialize()
{
CString csDllPath,csLeft;
TCHAR szPath[MAX_PATH];
int nPos;
szPath[0] = NULL;
GetModuleFileName(NULL,szPath,MAX_PATH);
csDllPath = szPath;
nPos = csDllPath.ReverseFind ('\\');
if(nPos != -1)
{
csLeft = csDllPath.Left (nPos);
csDllPath.Format ("%s\\%s",csLeft,DLLNAME);
}
else
{
csDllPath = DLLNAME;
}
m_hInstance = LoadLibrary(csDllPath);
if(m_hInstance)
{
m_egAddFn = (egAddFn) GetProcAddress (m_hInstance, "egAdd");
}
else
{
m_egAddFn = NULL;
return 0;
}
return 1;
}
int CWrapper::OnUnInitialize()
{
if(m_hInstance)
{
FreeLibrary(m_hInstance);
}
else
{
m_hInstance = NULL;
//Initialize all function pointers to NULL

m_egAddFn=NULL;
return 0;
}
return 1;
}

int CWrapper::egAdd(int a ,int b)
{
if (m_egAddFn)
{
return m_egAddFn (a,b);
}
return 0;
}

MFC DLL with wrapper

1. Create a MFC DLL with the project name "MyDLL"
2. Add a new class with class name "CMyClass" with class type "Generic Class".
3. Edit the following files as the instruction given below.
   

// Add the following lines in MyClass.h
class CMyClass
{
public:
int Add(int a , int b); //add this Line
};


// Add the following lines in MyDLL.h
#include "MyClass.h"
#ifndef EXP
#define EXP extern "C" __declspec( dllexport )
#endif
#define APPPTR ((CMyDLLApp*) AfxGetApp())
class CMyDLLApp : public CWinApp
{
public:
CMyClass m_MyObj; //add this line
};


// Add the following lines in MyClass.cpp:
#include "stdafx.h"
#include "MyDLL.h"
#include "MyClass.h"
int CMyClass::Add(int a , int b)
{
return(a+b);
}



// Add the following lines in MyDLL.cpp
#include "stdafx.h"
#include "MyDLL.h"
#include "MyClass.h"

EXP int egAdd(int a, int b)
{
int c=0;
c= APPPTR->m_MyObj.Add(a,b);
return c;
}