VC++写一个演示如何为应用程序写plugin插件的项目

布满荆棘的人生 2022-11-26 01:54 112阅读 0赞

如果不需要plugin，DLL一般都是带lib直接编译进项目的居多，这种情况下，和普通的函数库调用没什么区别。

但如果考虑到自己的应用程序中，要允许客户中任何人添加plugin，那情况就有所不同。

这里（参考地址：[http://www.cplusplus.com/articles/48TbqMoL/][http_www.cplusplus.com_articles_48TbqMoL]）给出了一个用MINGW编译的例子，但这个例子在VC上是运行不通的。我稍加修改，并作了备注，做成了一个VCC演示工程。main.hpp中例出了3种情况，

（1）extern "C" \_\_declspec(dllimport/dllexport)的C程序格式

（2）\_\_declspec(dllimport/dllexport)，可调用C++类的程序格式

（3）\*.def定义的形式

#ifndef __MAIN_HPP_INCLUDED__
    #define __MAIN_HPP_INCLUDED__
    
    #include <memory>
    #include <string>
    
    /*
    method (1)Only suitable for C type, NOT c++ classes
        #define DLLAPI extern "C" __declspec(dllexport)
    
    method (2) for compile with test1.lib / test2.lib / test3.lib etc.
        #define DLLAPI __declspec(dllexport)
    
        NOTE: if your application is not compiled with *.lib, and you need to use loadlibrary, the format may be strange as below
    
        typedef std::unique_ptr<Base> (__cdecl *ObjProc)(void);
        HINSTANCE mod = LoadLibrary("test1.dll");
        ObjProc objFunc = (ObjProc) GetProcAddress(mod, "?getObj@@YA?AV?$unique_ptr@VBase@@U?$default_delete@VBase@@@std@@@std@@XZ");
    
        the strange name ""?getObj@@YA?AV?$unique_ptr..." can be obtained from dumpbin tool
        dumpbin /exports test1.dll
        
    method (3) plugin mode
        #define DLLAPI
    
        NOTE: in this case you need to define the source.def file, the contents may be as below,
    
        LIBRARY TEST1
        EXPORTS
        getObj
        getName
        getValue
    */
    
    #ifdef _WINDLL // BUILD_DLL for MINGW
        //#define DLLAPI extern "C" __declspec(dllexport)
        //#define DLLAPI __declspec(dllexport)
        #define DLLAPI
    #else
        //#define DLLAPI extern "C" __declspec(dllimport)
        //#define DLLAPI __declspec(dllimport)
        #define DLLAPI
    #endif // BUILD_DLL
    
    
    class Base {
    public:
        virtual ~Base() = default;
        virtual void print(void) = 0;
        virtual double calc(double val) = 0;
    };
    
    // DLL export funcs
    
    DLLAPI std::unique_ptr<Base> getObj(void);
    DLLAPI std::string getName(void);
    DLLAPI int getValue(void);
    
    #endif // __MAIN_HPP_INCLUDED__

主要定义上变化的部分就在这里，其他内容就不再解释了，和原贴基本没什么区别，其实都很简单，例如main.cpp只添加了一个测试getValue函数，

// Program to demonstrate the use of a plugin system.
    
    #include <iostream>
    #include <vector>
    #include <memory>
    #include <stdexcept>
    #include <exception>
    #include <windows.h>
    #include "main.hpp"
    
    // Load the objects from the plugin folder.
    //
    // Takes as a parameter a reference to a list of modules,
    // which will be emptied and then refilled with handles to
    // the modules loaded. These should be freed with the
    // FreeLibrary() after use.
    //
    // Returns a list of Base*, contained in a smart pointer
    // to ease memory deallocation and help prevent memory
    // leaks.
    std::vector<std::unique_ptr<Base>> getPlugins(std::vector<HINSTANCE>& modules) {
        // A temporary structure to return.
        std::vector<std::unique_ptr<Base>> ret;
        // empty the modules list passed
        modules.clear();
    
        // Find the files contained in the 'plugins' folder
        WIN32_FIND_DATA fileData;
        HANDLE fileHandle = FindFirstFile(R"(.\plugins\*.dll)", &fileData);
    
        if (fileHandle == (void*)ERROR_INVALID_HANDLE ||
            fileHandle == (void*)ERROR_FILE_NOT_FOUND) {
            // If we couldn't find any plugins, quit gracefully,
            // returning an empty structure.
            return std::vector<std::unique_ptr<Base>>();
        }
    
        // Loop over every plugin in the folder and store in our
        // temporary return list
        do {
            // Define the function types for what we are retrieving
            typedef std::unique_ptr<Base> (__cdecl *ObjProc)(void);
            typedef std::string (__cdecl *NameProc)(void);
            typedef int (__cdecl *valueProc)(void);
    
            // Load the library
            HINSTANCE mod = LoadLibrary((R"(.\plugins\)" + std::string(fileData.cFileName)).c_str());
    
            if (!mod) {
                // Couldn't load the library, cleaning module list and quitting.
                for (HINSTANCE hInst : modules)
                    FreeLibrary(hInst);
                throw std::runtime_error("Library " + std::string(fileData.cFileName) + " wasn't loaded successfully!");
            }
    
            // Get the function and the class exported by the DLL.
            // If you aren't using the MinGW compiler, you may need to adjust
            // this to cope with name mangling (I haven't gone into this here,
            // look it up if you want).
            ObjProc objFunc = (ObjProc) GetProcAddress(mod, "getObj");
            int ecode = GetLastError();
            NameProc nameFunc = (NameProc) GetProcAddress(mod, "getName");
            ecode = GetLastError();
            valueProc valueFunc = (valueProc)GetProcAddress(mod, "getValue");
            ecode = GetLastError();
    
    
            if (!objFunc || !nameFunc)
                throw std::runtime_error("Invalid Plugin DLL: both 'getObj' and 'getName' must be defined.");
    
            // push the objects and modules into our vectors
            ret.push_back(objFunc());
            modules.push_back(mod);
    
            std::clog << nameFunc() << " loaded!\n";
        } while (FindNextFile(fileHandle, &fileData));
    
        std::clog << std::endl;
    
        // Close the file when we are done
        FindClose(fileHandle);
        return ret;
    }
    
    int main() {
        // Our list of modules. We need this to properly free the module
        // after the program has finished.
        std::vector<HINSTANCE> modules;
    
        // Enter a block, to prevent the Base objects being
        // deallocated after the modules are freed (which will
        // cause your program to crash)
        {
            // The list of objectects that we will retrieve from the DLL's.
            std::vector<std::unique_ptr<Base>> objs;
    
            // Load the plugins using our function
            try {
                objs = getPlugins(modules);
            } catch (const std::exception& e) {
                std::cerr << "Exception caught: " << e.what() << std::endl;
                return 1;
            }
    
            // Call the 'print' function for out classes.
            // This is normally where you would implement
            // the code for using the plugins.
            for (auto& x : objs) {
                x->print();
                std::cout << "\t" << x->calc(10) << std::endl;
            }
        }
    
        // Program finishing, time to clean up
        for (HINSTANCE hInst : modules)
            FreeLibrary(hInst);
    
        return 0;
    }

不想找的就直接到下面的链接下载VC++项目吧。

下载地址：[VC++写的演示如何为应用程序写plugin插件的项目][VC_plugin]

[https://download.csdn.net/download/tanmx219/12701204][VC_plugin]

[http_www.cplusplus.com_articles_48TbqMoL]: http://www.cplusplus.com/articles/48TbqMoL/
[VC_plugin]: https://download.csdn.net/download/tanmx219/12701204