製作外掛系統

// A list to store our DLL handles
std::vector<HINSTANCE> modules;
// The data for each file we find.
WIN32_FIND_DATA fileData;

// Find the first DLL file in out plugins folder,
// and store the data in out fileData structure.
HANDLE fileHandle = FindFirstFile(R"(.\plugins\*.dll)", &fileData);

if (fileHandle == (void*)ERROR_INVALID_HANDLE ||
    fileHandle == (void*)ERROR_FILE_NOT_FOUND) {
    // We couldn't find any plugins, lets just
    // return for now (imagine this is in main)
    return 0;
}

// Loop over every plugin in the folder, and store
// the handle in our modules list
do {
    // Load the plugin. We need to condense the plugin
    // name and the path together to correctly load the
    // file (There are other ways, I won't get into it here)
    HINSTANCE temp = LoadLibrary((R"(.\plugins\)" + 
                         std::string(fileData.cFileName)) .c_str());

    if (!temp) {
        // Couldn't load the library, continue on
        cerr << "Couldn't load library " << fileData.cFileName << "!\n";
        continue;
    }

    // Add the loaded module to our list of modules
    modules.push_back(temp);
// Continue while there are more files to find
} while (FindNextFile(fileHandle, &fileData));

for (HINSTANCE hInst : modules)
    FreeLibrary(hInst);

do {
    ...

    modules.push_back(temp);
    
    // Typedefs for the functions. Don't worry about the
    // __cdecl, that is for the name mangling (look up
    // that if you are interested).
    typedef std::unique_ptr<Base> (__cdecl *ObjProc)(void);
    typedef std::string (__cdecl *NameProc)(void);

    // Load the functions. This may or may not work, based on
    // your compiler. If your compiler created a '.def' file
    // with your DLL, copy the function names from that to
    // these functions. Look up 'name mangling' if you want
    // to know why this happens.
    ObjProc objFunc = (ObjProc)GetProcAddress(temp, "_Z6getObjv");
    NameProc nameFunc = (NameProc)GetProcAddress(temp, "_Z7getNamev");

    // use them!
    std::cout << "Plugin " << nameFunc() << " loaded!\n";
    std::unique_ptr<Base> obj = objFunc();
    obj->print();
    std::cout << "\t" << obj->calc() << std::endl;
} while (...);

extern "C" DLLAPI BOOL APIENTRY DllMain(HINSTANCE hInst, 
                                        DWORD reason, 
                                        LPVOID reserved)
{
    switch (reason) {
        case DLL_PROCESS_ATTACH:
            // attach to process, return FALSE to fail
        break;

        case DLL_PROCESS_DETACH:
            // detaching from process
        break;

        case DLL_THREAD_ATTACH:
            // attach to thread within process
        break;

        case DLL_THREAD_DETACH:
            // detach from thread within process
        break;
    }

    // return success
    return TRUE;
}

#ifdef __cplusplus  // if we are compiling C++
extern "C" {        // export the functions with C linkage
#endif

// ... your DLL exported functions, e.g.
const char* getName(void);

#ifdef __cplusplus
}
#endif 

// ...

const std::string pluginName = "TestPlugin";

extern "C"
const char* getName(void) {
    // just extrapolating on information given above: we can still
    // use the C++ Standard Library within functions, just you can't
    // pass them as the return value or function arguments
    return pluginName.c_str();
}