編寫共享庫的注意事項

1、共享庫的對外接口函數的聲明必須加上extern “C”。
2、使用共享庫對話接口函數生成的對象指針時在該對象未被釋放之前不能關閉共享庫句柄，否則會出現segmentation fault錯誤。

以下是一個插件式設計的示例

主執行程序：main.cpp

#include <iostream>
#include <dlfcn.h>
#include "SMSGamePlugin.h"

int main(int argc, char** argv)
{ 
    void *GameLib = dlopen("./Flower.so", RTLD_LAZY);
    const char *dlError = dlerror();
    if (dlError)
    { 
        std::cout << "dlopen error!" << dlError << std::endl;
        return(-1);
    }
    CSMSGamePlugin *(*pGetGameObject)(void);
    pGetGameObject = (CSMSGamePlugin *(*)(void))dlsym(GameLib, "GetGameObject");
    dlError = dlerror();
    if (dlError)
    { 
        std::cout << "dlsym error!" << dlError << std::endl;
        return(-1);
    }
    CSMSGamePlugin *pGame = (*pGetGameObject)();
    pGame->Initialize();
    pGame->Load();
    pGame->Handle();
    delete *pGame;
    dlclose(GameLib);
}

公用基類部分：SMSGamePlugin.h

#ifndef __SMSGamePlugin_h__
#define __SMSGamePlugin_h__

class CSMSGamePlugin
{ 
public:
    virtual int Initialize(void) = 0;
    virtual int Load(void) = 0;
    virtual int Handle(void) = 0;
};

#endif

編譯：g++ -rdynamic -ldl -s -o Test main.cpp

共享庫部分：

共享庫頭文件：Flower.h

#ifndef __Flower_h__
#define __Flower_h__

#include "SMSGamePlugin.h"

extern "C" CSMSGamePlugin *GetGameObject(void);

class CFlower: public CSMSGamePlugin
{ 
public:
    virtual int Initialize(void);
    virtual int Load(void);
    virtual int Handle(void);
};

#endif

共享庫實現文件：Flower.cpp

#include <iostream>
#include "Flower.h"

CSMSGamePlugin *GetGameObject(void)
{ 
    return(new CFlower());
}

int CFlower::Initialize(void)
{ 
    std::cout << "Initialize()" << std::endl;
    return(0);
}

int CFlower::Load(void)
{ 
    std::cout << "Load()" << std::endl;
    return(0);
}

int CFlower::Handle(void)
{ 
    std::cout << "Handle()" << std::endl;
    return(0);
}

編譯：g++ -c Flower.cpp
g++ -shared -o Flower.so

注意：如果不加extern "C"編譯后運行時就會提示：
dlsym error!./Test: undefined symbol: GetGameObject