Deep analysis of creating DLLS in VC exporting global variables functions and classes

One. Create DLL
1. Create a new Win32 empty project MathLib in VC;
2. Add precompiled header file stdafx.h, define import and export control symbol:

//stdafx.h
#pragma once
#define MATHLIB_EXPORT

3. Add the header file mathlib.h containing the global variables, functions and classes to be exported:

 //MathLib.h
 #pragma once

 #ifdef MATHLIB_EXPORT
 #define MATHLIBAPI __declspec(dllexport)
 #else
 #define MATHLIBAPI __declspec(dllimport)
 #endif

 //macro
 #define PI 3.14149

 //Global variable
 extern MATHLIBAPI int GlobalVariable;

 //Function
 MATHLIBAPI int Add(int a,int b);

 //Class
 class MATHLIBAPI Math
 {
 public:
  int Multiply(int a,int b);
 };

4. Add the implementation file mathlib.cpp for the exported elements

 //MathLib.cpp
 #include "stdafx.h"
 #include "MathLib.h"

 int GlobalVariable = 100;

 int Add(int a,int b)
 {
  return a+b;
 }

 int Math::Multiply(int a,int b)
 {
  return a*b;
 }

Second, test the DLL created
Test code:

 #include "stdafx.h"
 #include <iostream>
 using namespace std;

 #include "../MathLib/MathLib.h"
 #pragma comment(lib,"../Debug/MathLib.lib")

 int _tmain(int argc, _TCHAR* argv[])
 {
  cout<<"Pi = "<<PI<<endl;

  cout<<"GlobalVariable = "<<GlobalVariable<<endl;

  int a = 20,b = 30;
  cout<<"a="<<a<<", "<<"b="<<b<<endl;
  cout<<"a+b = "<<Add(a,b)<<endl;

  Math math;
  cout<<"a*b = "<<math.Multiply(a,b)<<endl;

  return 0;
 }