C/C++ DLL 简单实现

// dllmain.cpp : 定义 DLL 应用程序的入口点。
#include "pch.h"
BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}
extern "C"
{
    __declspec(dllexport) int add(int a, int b);
    __declspec(dllexport) int sub(int a, int b);
}
int add(int a, int b)
{
    return a + b;
}
int sub(int a, int b)
{
    return a - b;
}

#include <iostream>
#include <Windows.h>
//声明函数指针，指向找到的函数地址，后面通过函数指针调用DLL中定义的函数
typedef int(*FUN_ADD)(int, int);
typedef int(*FUN_SUB)(int, int);
int main()
{
  HMODULE hModule = LoadLibrary(L"C:/Users/test_2/source/repos/Dll2/Release/Dll2.dll");
  if (hModule == nullptr)
  {
    std::cout << "加载DLL失败！\n";
    return 0;
  }
  auto dllFunAdd = (FUN_ADD)GetProcAddress(hModule, "add");
  auto dllFunSub = (FUN_ADD)GetProcAddress(hModule, "sub");
  if (dllFunAdd == nullptr || dllFunSub == nullptr)
  {
    std::cout << "加载函数失败！\n";
    return 0;
  }
  std::cout << "3 add 2 :" << dllFunAdd(3, 2) << std::endl;
  std::cout << "4 sub 2 :" << dllFunSub(4, 2) << std::endl;
  FreeLibrary(hModule);
  system("pause");
  return 0;
}