boost::shared_ptr Assertion error with boost::asio:io_service

Question

I am currently trying to understand the boost::asio-API. in one of my classes I use a boost::shared_ptr to reference an io_service in this way:

class myClass : public boost::asio::serial_port
{
public: 
    myClass(std::string Port);

private:
    boost::shared_ptr<boost::asio::io_Service> _io_service_ptr;
};

And the implementation according to that is:

myClass::myClass(std::string Port) : _io_service_ptr(new boost::asio::io_service), 
boost::asio::serial_port(*_io_service_ptr, Port)
{
    //do stuff
}

When I do this, i get the error: Assertion failed! px != 0 [...]

When use the same pattern for other boost::asio objects (like boost::asio::io_service::work(service)) it works fine. What did i do wrong with the io_service?

Answer 1

Base classes are initialised before members, so the io_service is not created until after you try to dereference the uninitialised pointer to pass a reference to the base class.

But deriving from serial_port seems rather odd; why not use aggregation instead? Make sure the service is declared before anything that uses it:

class myClass {
public:
    myClass(std::string port) : serial_port(io_service, port) {}

    // public interface to interact with the serial port and whatever else

private:
    boost::asio::io_service io_service; // or a shared pointer if there's a good reason
    boost::asio::serial_port serial_port;
};

It's also likely that you'd want to share one service with many objects, so perhaps it shouldn't be owned by this class at all:

class myClass {
public:
    myClass(boost::asio::io_service & io_service, std::string port) : 
        serial_port(io_service, port) 
    {}

    // public interface to interact with the serial port and whatever else

private:
    boost::asio::serial_port serial_port;
};