A class to wrap DLL functions

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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 :)

Revision History

26 Jun 2002 - Initial Revision