从DLL中导出变量

缺乏、安全感 2022-06-07 04:42 199阅读 0赞

## [DLL入门浅析（3）——从DLL中导出变量][DLL_3_DLL] ##

前面介绍了怎么从DLL中导出函数，下面我们来看一下如何从DLL中导出变量来。

声明为导出变量时，同样有两种方法：  
   第一种是用\_\_declspec进行导出声明

![None.gif][]\#ifndef \_DLL\_SAMPLE\_H  
![None.gif][] \#define \_DLL\_SAMPLE\_H  
![None.gif][]  
![None.gif][] //  如果定义了C++编译器，那么声明为C链接方式   
![None.gif][]\#ifdef \_\_cplusplus  
![ExpandedBlockStart.gif][] extern "C"  \{  
![InBlock.gif][]\#endif  
![InBlock.gif][]  
![InBlock.gif][]// 通过宏来控制是导入还是导出  
![InBlock.gif][]\#ifdef \_DLL\_SAMPLE  
![InBlock.gif][]\#define DLL\_SAMPLE\_API \_\_declspec(dllexport)  
![InBlock.gif][]\#else  
![InBlock.gif][]\#define DLL\_SAMPLE\_API \_\_declspec(dllimport)  
![InBlock.gif][]\#endif  
![InBlock.gif][]  
![InBlock.gif][]// 导出/导入变量声明  
![InBlock.gif][]DLL\_SAMPLE\_API extern int DLLData;  
![InBlock.gif][]  
![InBlock.gif][]\#undef DLL\_SAMPLE\_API  
![InBlock.gif][]  
![InBlock.gif][]\#ifdef \_\_cplusplus  
![ExpandedBlockEnd.gif][]\}  
![None.gif][] \#endif  
![None.gif][]  
![None.gif][] \#endif  
![None.gif][]

第二种是用模块定义文件（.def）进行导出声明

![None.gif][]LIBRARY DLLSample  
![None.gif][]DESCRIPTION "my simple DLL"  
![None.gif][]EXPORTS  
![None.gif][]        DLLData DATA  ；DATA表示这是数据（变量）

下面是DLL的实现文件

![None.gif][]\#include "stdafx.h"  
![None.gif][] \#define \_DLL\_SAMPLE  
![None.gif][]  
![None.gif][]\#ifndef \_DLL\_SAMPLE\_H  
![None.gif][]\#include "DLLSample.h"  
![None.gif][] \#endif  
![None.gif][]  
![None.gif][]\#include "stdio.h"  
![None.gif][]  
![None.gif][] int DLLData;  
![None.gif][]  
![None.gif][] // APIENTRY声明DLL函数入口点   
![None.gif][]BOOL APIENTRY DllMain(HANDLE hModule, DWORD ul\_reason\_for\_call, LPVOID lpReserved)  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]　switch (ul\_reason\_for\_call)  
![ExpandedSubBlockStart.gif][]　\{  
![InBlock.gif][]　　case DLL\_PROCESS\_ATTACH:  
![InBlock.gif][]      DLLData = 123;  // 在入口函数中对变量进行初始化  
![InBlock.gif][]      break  
![InBlock.gif][]　　case DLL\_THREAD\_ATTACH:  
![InBlock.gif][]　　case DLL\_THREAD\_DETACH:  
![InBlock.gif][]　　case DLL\_PROCESS\_DETACH:  
![InBlock.gif][]　　　break;  
![ExpandedSubBlockEnd.gif][]　\}  
![InBlock.gif][]　return TRUE;  
![ExpandedBlockEnd.gif][]\}  
![None.gif][]

同样，应用程序调用DLL中的变量也有两种方法。  
第一种是隐式链接：

![None.gif][]\#include <stdio.h>  
![None.gif][]\#include "DLLSample.h"  
![None.gif][]  
![None.gif][]\#pragma comment(lib,"DLLSample.lib")  
![None.gif][]  
![None.gif][]  
![None.gif][] int main( int argc,  char \*argv\[\])  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]　printf("%d ", DLLSample);  
![InBlock.gif][]　return 0;  
![ExpandedBlockEnd.gif][]\}  
![None.gif][]  
![None.gif][]

第二种是显式链接：

![None.gif][]\#include <iostream>  
![None.gif][]\#include <windows.h>  
![None.gif][]  
![None.gif][] int main()  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]        int my\_int;  
![InBlock.gif][]        HINSTANCE hInstLibrary = LoadLibrary("DLLSample.dll");  
![InBlock.gif][]  
![InBlock.gif][]        if (hInstLibrary == NULL)  
![ExpandedSubBlockStart.gif][]        \{  
![InBlock.gif][]         FreeLibrary(hInstLibrary);  
![ExpandedSubBlockEnd.gif][]        \}  
![InBlock.gif][]        my\_int = \*(int\*)GetProcAddress(hInstLibrary, "DLLData");  
![InBlock.gif][]        if (dllFunc == NULL)  
![ExpandedSubBlockStart.gif][]        \{  
![InBlock.gif][]         FreeLibrary(hInstLibrary);  
![ExpandedSubBlockEnd.gif][]        \}  
![InBlock.gif][]        std::cout<<my\_int;  
![InBlock.gif][]        std::cin.get();  
![InBlock.gif][]        FreeLibrary(hInstLibrary);  
![InBlock.gif][]        return(1);  
![ExpandedBlockEnd.gif][]\}  
![None.gif][]

通过GetProcAddress取出的函数或者变量都是地址，因此，需要解引用并且转类型。

[DLL_3_DLL]: http://www.cppblog.com/suiaiguo/archive/2009/07/20/90643.html
[None.gif]: /images/20220607/d12bc37d878d421a8c5724a2f78d5e8b.png
[ExpandedBlockStart.gif]: /images/20220607/84b62b610f3942499b5bc57359931542.png
[InBlock.gif]: /images/20220607/8c37c3bac1654496bba2f7120db5ce80.png
[ExpandedBlockEnd.gif]: /images/20220607/e760b4757f2e4bd49416a9d7bf021c5f.png
[ExpandedSubBlockStart.gif]: /images/20220607/856b1b9e535c4ef8b02823f080fc82ee.png
[ExpandedSubBlockEnd.gif]: /images/20220607/9cd1dadc3c634b048cad9f117275fbdd.png