VC++DLL动态链接库程序
VC++DLL动态链接库程序
VC++DLL动态链接库程序
最近查找了一下VC++中关于编写DLL动态库的资料,主要是导出函数和导出类的编写。因为在实际项目开发中有时需要使用C++编写好DLL接口,控制设备,提供给其他语言如Nodejs、C#等使用。
C++ DLL 导出函数
使用VS2017等IDE生成dll程序,示例如下:
DllDemo
DllDemo.h
// 下列 ifdef 块是创建使从 DLL 导出更简单的
// 宏的标准方法。此 DLL 中的所有文件都是用命令行上定义的 DLLDEMO_EXPORTS
// 符号编译的。在使用此 DLL 的
// 任何其他项目上不应定义此符号。这样,源文件中包含此文件的任何其他项目都会将
// DLLDEMO_API 函数视为是从 DLL 导入的,而此 DLL 则将用此宏定义的
// 符号视为是被导出的。
#ifdef DLLDEMO_EXPORTS
#define DLLDEMO_API __declspec(dllexport)
#else
#define DLLDEMO_API __declspec(dllimport)
#endif
// 此类是从 DllDemo.dll 导出的
class DLLDEMO_API CDllDemo {
public:
CDllDemo(void);
// TODO: 在此添加您的方法。
};
extern DLLDEMO_API int nDllDemo;
// 加上extern "C"表示是一个C函数,不重载
extern "C" DLLDEMO_API int fnDllDemo(void);
DllDemo.cpp
// DllDemo.cpp : 定义 DLL 应用程序的导出函数。
//
#include "stdafx.h"
#include "DllDemo.h"
#include <iostream>
using namespace std;
// 这是导出变量的一个示例
DLLDEMO_API int nDllDemo=0;
// 这是导出函数的一个示例。
DLLDEMO_API int fnDllDemo(void)
{
cout << "fnDllDemo(void) called" << endl;
return 42;
}
// 这是已导出类的构造函数。
// 有关类定义的信息,请参阅 DllDemo.h
CDllDemo::CDllDemo()
{
cout << "CDllDemo::CDllDemo() called" << endl;
return;
}
dllmain.cpp
// dllmain.cpp : 定义 DLL 应用程序的入口点。
#include "stdafx.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;
}
DLL的测试程序
使用VS2017创建一个基于Win32的控制台应用程序testDllDemo:
testDllDemo.cpp
// testDllDemo.cpp : 定义控制台应用程序的入口点。
//
#include "stdafx.h"
#include <stdio.h>
#include <Windows.h>
typedef int(*dllpFun)(void);
int _tmain(int argc, _TCHAR* argv[])
{
HMODULE hDll = LoadLibrary(L"DllDemo.dll");
if (!hDll)
{
return -1;
}
dllpFun pFunc = (dllpFun)GetProcAddress(hDll, "fnDllDemo");
pFunc();
FreeLibrary(hDll);
getchar();
return 0;
}
C++ DLL 导出类
1.导出类中第一种方法:简单导出类(不推荐使用)
简单导出类的示例程序
NaiveApproach.h
//2011.10.6
//cswuyg
//dll导出类,比较差劲的方法
#pragma once
// The following ifdef block is the standard way of creating macros which make exporting
// from a DLL simpler. All files within this DLL are compiled with the NAIVEAPPROACH_EXPORTS
// symbol defined on the command line. this symbol should not be defined on any project
// that uses this DLL. This way any other project whose source files include this file see
// NAIVEAPPROACH_API functions as being imported from a DLL, whereas this DLL sees symbols
// defined with this macro as being exported.
#ifdef NAIVEAPPROACH_EXPORTS
#define NAIVEAPPROACH_API __declspec(dllexport)
#else
#define NAIVEAPPROACH_API __declspec(dllimport)
#endif
//基类也必须导出,否则警告:
class NAIVEAPPROACH_API CBase
{
public:
void Test();
private:
int m_j;
};
//也必须导出
class NAIVEAPPROACH_API CDate
{
public:
void Test2();
private:
int m_k;
};
class NAIVEAPPROACH_API CNaiveApproach : public CBase
{
public:
CNaiveApproach(int i = 0);
// TODO: add your methods here.
void Func();
private:
int m_iwuyg;
CDate m_dobj;
};
NaiveApproach.cpp
// NaiveApproach.cpp : Defines the entry point for the DLL application.
//
#include "stdafx.h"
#include "NaiveApproach.h"
#ifdef _MANAGED
#pragma managed(push, off)
#endif
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;
}
#ifdef _MANAGED
#pragma managed(pop)
#endif
// This is the constructor of a class that has been exported.
// see NaiveApproach.h for the class definition
CNaiveApproach::CNaiveApproach(int i) : m_iwuyg(i)
{
}
void CNaiveApproach::Func()
{
wcout << L" cswuyg test dll , i = " << m_iwuyg << endl;
system("pause");
}
void CBase::Test()
{
wcout << L"Just a Test" << endl;
system("pause");
}
void CDate::Test2()
{
wcout << L"Test 2" << endl;
system("pause");
}
UserDll.cpp
// User.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include "NaiveApproach.h"
#pragma comment(lib, "../debug/NaiveApproach.lib")
int _tmain(int argc, _TCHAR* argv[])
{
//////////////////////////////////////////////////////////////////////////
CNaiveApproach obj(10);
obj.Test();
obj.Func();
//////////////////////////////////////////////////////////////////////////
return 0;
}
简单导出类的缺点
这种简单导出类的方式,除了导出的东西太多、使用者对类的实现依赖太多以外,还有其他问题:必须保证使用同一种编译器。导出类的本质是导出类里的函数,因为语法上直接导出了类,没有对函数的调用方式、重命名进行设置,导致了产生的dll并不通用。
2.导出类的一种通用方法(推荐):使用接口
定义一个抽象类(都是纯虚函数),调用者跟dll共用一个抽象类的头文件,dll中实现此抽象类的派生类,dll最少只需要提供一个用于获取抽象类对象指针的接口。
写一个基类,方法都为虚函数,这样使用dll的exe使用都没问题。
dll的类从基类 派生,然后返回基类接口即可。
面向抽象设计优点:这种方式利用了C++类的虚函数,类似COM思想,采用接口跟实现分离,可以使得工程的结构更清晰,使用者只需要知道接口,而无需知道具体实现,产生的DLL通用没有特定环境限制。
注意事项:调用者跟DLL共用一个抽象类的头文件,调用者依赖于DLL的东西很少,只需要知道抽象类的接口,以及获取对象指针的导出函数,对象内存空间的申请和释放都在DLL模块中完成
导出类的较好方式 DLL示例程序
ExportClassImpl.h
//2011.10.6
//cswuyg
//dll导出类
// 实现类
#pragma once
#include "MatureApproach.h"
class ExportImpl : public IExport
{
public:
virtual void Hi();
virtual void Test();
virtual void Release();
~ExportImpl();
private:
};
MatureApproach.h
//2011.10.6
//cswuyg
//dll导出类
//dll跟其使用者共用的头文件
#pragma once
// The following ifdef block is the standard way of creating macros which make exporting
// from a DLL simpler. All files within this DLL are compiled with the MATUREAPPROACH_EXPORTS
// symbol defined on the command line. this symbol should not be defined on any project
// that uses this DLL. This way any other project whose source files include this file see
// MATUREAPPROACH_API functions as being imported from a DLL, whereas this DLL sees symbols
// defined with this macro as being exported.
#ifdef MATUREAPPROACH_EXPORTS
#define MATUREAPPROACH_API __declspec(dllexport)
#else
#define MATUREAPPROACH_API __declspec(dllimport)
#endif
class IExport
{
public:
virtual void Hi() = 0;
virtual void Test() = 0;
virtual void Release() = 0;
};
extern "C" MATUREAPPROACH_API IExport* _stdcall CreateExportObj();
extern "C" MATUREAPPROACH_API void _stdcall DestroyExportObj(IExport* pExport);
ExportClassImpl.cpp
#include "stdafx.h"
#include "ExportClassImpl.h"
void ExportImpl::Hi()
{
wcout << L"Hello World" << endl;
}
void ExportImpl::Test()
{
wcout << L"Hi cswuyg" << endl;
}
void ExportImpl::Release()
{
delete this;
}
ExportImpl::~ExportImpl()
{
cout << "Release OK" << endl;
}
MatureApproach.cpp
#include "stdafx.h"
#include "ExportClassImpl.h"
void ExportImpl::Hi()
{
wcout << L"Hello World" << endl;
}
void ExportImpl::Test()
{
wcout << L"Hi cswuyg" << endl;
}
void ExportImpl::Release()
{
delete this;
}
ExportImpl::~ExportImpl()
{
cout << "Release OK" << endl;
}
MatureApproach.def
LIBRARY "MatureApproach"
EXPORTS
CreateExportObj @ 1
DestroyExportObj @ 2
测试调用DLL的Win32控制台程序 UserDll.cpp
// User.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include "MatureApproach.h"
#pragma comment(lib, "../debug/MatureApproach.lib")
int _tmain(int argc, _TCHAR* argv[])
{
IExport* pExport = CreateExportObj();
pExport->Hi();
pExport->Test();
DestroyExportObj(pExport);
system("pause");
return 0;
}
参考资料
参考了相关的资料网址:
[HowTo: Export C++ classes from a DLL]: https://www.codeproject.com/Articles/28969/HowTo-Export-C-classes-from-a-DLL
[Explicitly Linking to Classes in DLL’s ]: http://www.codeguru.com/Cpp/W-P/dll/importexportissues/article.php/c123
[C++ DLL导出类 知识大全]: https://www.cnblogs.com/lidabo/p/7121745.html
[怎样从一个DLL中导出一个C++类]: https://blog.csdn.net/liubing8609/article/details/82156067
[DLL导出C++类]: https://blog.csdn.net/qq_33757398/article/details/82229325
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