怎么调用动态库_动态库导出类动态调用[通俗易懂]

头文件：
#pragma once
class MyAdd
{
public:
    MyAdd();
    virtual ~MyAdd();
    int add(int a, int b);
    float add(float a, float b);
};
源文件：
#include "MyAdd.h"
MyAdd::MyAdd()
{
}
MyAdd::~MyAdd()
{
}
int MyAdd::add(int a, int b)
{
    return a + b;
}
float MyAdd::add(float a, float b)
{
    return a + b;
}

头文件：
#include <stdlib.h>

#include "MyAdd.h"
#include "add_api.h"

int csvMyAddGetInstance(void ** ppHandle)
{
    MyAdd* p = new MyAdd();
    *ppHandle = p;
    return 0;
}

int csvMyAddReleaseInstance(void * ppHandle)
{
    MyAdd* p = (MyAdd*)(ppHandle);
    if (p != NULL)
    {
        delete p;
        p = NULL;
    }
    return 0;
}

int csvMyAddaddInt(void ** ppHandle, int a, int b)
{
    MyAdd* p = (MyAdd*)(ppHandle);
    if (p == NULL) return INT_MIN;
    
    return a + b;
}

float csvMyAddaddFloat(void ** ppHandle, float a, float b)
{
    MyAdd* p = (MyAdd*)(ppHandle);
    if (p == NULL) return INT_MIN;

    return a + b;
}

源文件：
#ifndef CSV_ADD_API_H

  #define CSV_ADD_API_H

  #ifdef CSVADDAPI_LIB
  #define CSVADDAPI_LIB_EXPORT extern “C” __declspec(dllexport)
  #else
  #define CSVADDAPI_LIB_EXPORT extern “C” __declspec(dllimport)
  #endif

  CSVADDAPI_LIB_EXPORT int csvMyAddGetInstance(void ** ppHandle);

  CSVADDAPI_LIB_EXPORT int csvMyAddReleaseInstance(void * ppHandle);

  CSVADDAPI_LIB_EXPORT int csvMyAddaddInt(void ** ppHandle, int a, int b);

  CSVADDAPI_LIB_EXPORT float csvMyAddaddFloat(void ** ppHandle, float a, float b);

  #endif //CSV_ADD_API_H

#include <iostream>
#include <stdlib.h>
#include <string>
#include<stdio.h>
#include <windows.h>
using namespace std;

/*通过LoadLibraryA 和 GetProcAddress，动态调用无需配置链接库lib和相关的头文件*/

typedef int(*MyAddGetInstance)(void **ppHandle);              //定义类型：获取加法类的函数指针
typedef int(*MyAddReleaseInstance)(void *ppHandle);           //定义类型：声明释放加法类的函数指针
typedef int(*MyAddAddInt)(void **ppHandle, int a, int b);     //定义类型：声明整数的加法函数指针

int main(int argc, char** argv)
{
    /*导入DLL库*/ 
    string dll_path = "MyDll.dll";
    HINSTANCE phandle = LoadLibraryA(dll_path.c_str());

    /*获取 DLL库内部的函数句柄*/ 
    MyAddGetInstance csvMyAddGetInstance;
    csvMyAddGetInstance = (MyAddGetInstance)GetProcAddress(phandle, "csvMyAddGetInstance");
    MyAddReleaseInstance csvMyAddReleaseInstance;
    csvMyAddReleaseInstance = (MyAddReleaseInstance)GetProcAddress(phandle, "csvMyAddReleaseInstance");
    MyAddAddInt myAddAddInt;
    myAddAddInt = (MyAddAddInt)GetProcAddress(phandle, "csvMyAddaddInt");

    /*调用函数*/ 
    void* pinst = NULL;
    csvMyAddGetInstance(&pinst);    
    int res = myAddAddInt(&pinst, 1, 3);    
    csvMyAddReleaseInstance(pinst);

    cout << res << endl;

    system("pause");
    return  0;
}