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A class to wrap DLL functions

By , 25 Jun 2002
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Introduction

My project needs to manage a large set of DLLs. All of them export a same set of functions. None of them link with the main project at compile time. We call them PlugIns. These plugins are used to extend the ability of the main program. Once they are copied into the program directory, the program can use them, and if they are removed from the directory, the main program works just fine, except that some functions cannot be used.

Since these DLLs are not available at the time that the main program is compiled, we have to use LoadLibrary, GetProcAddress and FreeLibrary to use these DLLs. It's really boring! I needed a class to ease this job. In fact, these DLLs looks just like classes (they all have the same interface: a set of functions). Using a class to wrap these DLLs is just reasonable.

Here comes the class CDLLModule. This class is only for deriving. Let's see how to use it first. Suppose you have a DLL which export two functions like this:

 
    int WINAPI GetEngine(char *szEngineType, char *szEngineVersion);
    int WINAPI StartEngine(HWND hWnd);

The wrapper class would like this:

class CMyClass : public CDLLModule
{
    DECLARE_DLL_FUNCTION(int, WINAPI,
                          GetEngine, (char *, char *))
    DECLARE_DLL_FUNCTION(int, WINAPI,
                                  StartEngine, (HWND))

    BEGIN_DLL_INIT()
        INIT_DLL_FUNCTION(int, WINAPI,
             GetEngine, (char *, char *), "GetEngine")
        INIT_DLL_FUNCTION(int, WINAPI,
                   StartEngine, (HWND), "StartEngine")
    END_DLL_INIT()
};

Then we can use it like this:

    CMyClass    module;
    module.Init("MyDLL.dll");
    module.GetEngine(m_str1, m_str2);
    module.StartEngine(m_hWnd);

I should explain it in more detail, but I am really not good at English. Anyway, the code is very simple, only 64 lines including comments. I think it's very useful, and I hope you think so too.

One last thing. It's a good idea to check the validation of the function before calling. In another word, if you are not sure that all functions are exported well from the DLL, Call it like this:

    if (module.GetEngine)
        module.GetEngine(m_str1, m_str2);

Enjoy Smile | :)

Revision History

26 Jun 2002 - Initial Revision

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

Neil Yao

China China
I'm a chinese programer living in Shanghai, currently working for a software company whose main business is to deliver computer based testing. Software simulation for computer based testing and certifications is my main responsibility in this company. Execpt for software development, I like out-door activities and photography. I am willing to make friends in China and all over the world, so contact me if you have anything in common with meSmile | :)

Comments and Discussions

 
QuestionFreeLibrary function VS 2005 - WXP Pinmemberpicm24-Apr-10 1:30 
GeneralHummmmmm PinmemberKelly Cristina Mara2-Mar-08 12:10 
Could you teach more about DLL?
 
I will be wait for:
 
Kellyc.mara2007@hotmail.com
GeneralMeaning of the second parametr DECLARE_DLL_FUNCTION Pinmemberbadzio23-Feb-07 2:40 
GeneralRe: Meaning of the second parametr DECLARE_DLL_FUNCTION Pinmemberbadzio23-Feb-07 2:57 
GeneralDLL code Pocket PC PinmemberZiggy2k27-Sep-05 6:26 
GeneralRe: DLL code Pocket PC PinmemberNeil Yao27-Sep-05 18:56 
GeneralOPSEC SDK PinsussAnonymous24-May-05 5:34 
QuestionWhat abt Consructor and others?? PinmemberPradip K. Jadav4-Mar-05 19:42 
QuestionHow to calling this DLL into VB6 Pinmemberalejorb7-Aug-04 6:48 
AnswerRe: How to calling this DLL into VB6 PinmemberYao Zhifeng8-Aug-04 15:45 
Generaltanx Pinmemberasd175325-Nov-03 10:41 
GeneralRe: tanx PinmemberRalph Wetzel9-Apr-04 2:29 
Generalcannot access private member declared in class 'CDLLClass' Pinmemberposbis9-Sep-03 10:43 
GeneralRe: cannot access private member declared in class 'CDLLClass' Pinmemberposbis9-Sep-03 10:58 
GeneralRe: cannot access private member declared in class 'CDLLClass' PinmemberYao Zhifeng9-Sep-03 14:59 
Questionhow to use it with no arguements Pinmembernikhilpp8-Aug-03 7:43 
AnswerRe: how to use it with no arguements PinmemberYao Zhifeng11-Aug-03 15:05 
GeneralSuggestion to use typedef in the macros PinmemberAndrew Schetinin5-Jul-03 22:45 
GeneralI forgot about UNICODE too PinmemberAndrew Schetinin5-Jul-03 22:51 
Generalcreating a Game engine DLL Pinmembersriniatig10-Apr-03 22:57 
GeneralRe: creating a Game engine DLL PinmemberYao Zhifeng13-Apr-03 15:38 
GeneralRe: creating a Game engine DLL PinmemberAndrew Schetinin3-Jul-03 3:36 
GeneralHeader From lib Pinmemberbfadi2-Mar-03 14:15 
GeneralDebug Error! PinsussJack Furr14-Feb-03 22:19 
GeneralRe: Debug Error! PinsussJack Furr15-Feb-03 15:14 

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