Question

我尝试使用dlopen（）API在运行时加载共享对象（SensorTemp派生类）。当我尝试将指针指向适当的函数指针时，我得到

LinkTest.cpp:26:48: error: invalid static_cast from type ‘void*’ to type ‘Sensor*()’
Sensor* mySensor = static_cast<Sensor *()>(mkr)(myHub, a, b, c, d, e);

这里是相关的Sensor.h基类构造函数：

class Sensor
{
public:
    Sensor(Hub& _pHub, const std::string& _name, const std::string& _type, const std::string& _logLevel, const std::string& _configInfo, const std::string& _location): m_pHub(&_pHub), m_name(_name), m_type(_type), m_logLevel(_logLevel), m_configInfo(_configInfo), m_location(_location) {}

派生类SensorTemp.h :(其CTOR称之为基础CTOR）

#include "Sensor.h"

class SensorTemp : public Sensor
{
public:
    SensorTemp(Hub& _pHub,  const std::string& _name, 
                            const std::string& _type, 
                            const std::string& _logLevel, 
                            const std::string& _configInfo, 
                            const std::string& _location);
    ~SensorTemp() {}
    void* Run();
private:
    int m_lowTemp;
    int m_highTemp;
    int m_interval;
};

extern "C"
{
    SensorTemp* Create(Hub& _pHub,  const std::string& _name, 
                                    const std::string& _type, 
                                    const std::string& _logLevel, 
                                    const std::string& _configInfo, 
                                    const std::string& _location)
    {
        return new SensorTemp(_pHub, _name, _type, _logLevel, _configInfo, _location);
    }

}

#endif //__SENSORTEMP_H__

测试：

int main(int argc, char **argv)
{
    Hub myHub;
    string a = "A";
    string b = "B";
    string c = "C";
    string d = "D";
    string e = "E";
    string f = "F";
    void *hndl = dlopen("./libSensorTemp.so", RTLD_LAZY);
    if(hndl == NULL)
    {
       std::cerr << dlerror() << std::endl;
       exit(-1);
    }
    void *mkr = (Sensor*)dlsym(hndl, "Create");
    Sensor* mySensor = static_cast<Sensor *()>(mkr)(myHub, a, b, c, d, e);
    mySensor->Run();

}

Answer 1

你对指向函数的指针是错误的。你的代码应该是：

void *mkr = (void *)dlsym(hndl, "Create"); // only the address matters here
Sensor* mySensor = static_cast<Sensor *(*)(Hub&, const std::string&, const std::string&,
    const std::string&, const std::string&, const std::string&)>(mkr)(myHub, a, b, c, d, e);
mySensor->Run();

因为您希望将mkr转换为一个指向函数的指针，该函数接受一个Hub引用和5个string引用并返回指向Sensor的指针

Answer 2

参考this question，这是一个简化的例子：

#include <dlfcn.h>
#include <string>

class Sensor;
class Hub;

extern "C"
{
    Sensor* Create(Hub& _pHub
        , const std::string& _name
        , const std::string& _type
        , const std::string& _logLevel
        , const std::string& _configInfo
        , const std::string& _location)
    {
        return nullptr;
    }
}



int main(int argc, char **argv)
{
    void *hndl = dlopen("./libSensorTemp.so", RTLD_LAZY);
    if(hndl == NULL) {
       exit(-1);
    }

    void *mkr = (Sensor*)dlsym(hndl, "Create");

    typedef Sensor*(*create_fn)(Hub&
        , const std::string&
        , const std::string&
        , const std::string&
        , const std::string&
        , const std::string&);

    create_fn creator = 0;
    *reinterpret_cast<void**>(&creator) = mkr;

    // ....
}

在运行时加载.so的c ++静态转换

2 个答案: