Re: [Boost-users] class initialization problem

Subject: Re: [Boost-users] class initialization problem
From: Krzysztof Żelechowski (giecrilj_at_[hidden])
Date: 2011-10-01 04:50:04

Christopher Pisz wrote:

> 
> I have a Server class inherited from a Listener class, with the latter
> being bases on the boost::asio example code.
> 
> My problem is that the Listener class requires am boost::asio::io_service
> & in order to initialize its member variables.
> 
> I wanted the Server class to be responsible for starting a thread, owning
> the io_service, and running it.
> 
> It seems I cannot do that!
> 
> class Server : public Listener
> {
> public:
>    Server()
>       :
>       Listener(ioService_)
>    {
>    }
>    
>    // Snip
> 
> protected:
> 
>    boost::asio::io_service ioService_;
> };
> 
> 
> class Listener
> {
> public:
> 
>    Listener(boost::asio::io_service & ioService)
>       :
>       socket_(ioService)
>    {
>    }
> 
>    // Snip
> 
> protected:
>    boot::asio::ip::tcp::socket socket_;
> };
> 
> The above throws an unhandled exception in the initialization of the
> derived class.
> 
> I suppose this is because ioService_ is not constructed yet? Since the C++
> rules, if I remember correctly, say the base class gets constructed before
> the members of the derived?
> 
> 
> So, I tried:
> 
> Server()
>       :
>       ioService_(),
>       Listener(ioService_)
>    {
>    }
> 
> to try and force it, but it still throws an exception.
> 
> The only way to get it to not throw an exception is to create the instance
> to io-service in main() and then pass it as a reference into the class
> constructor. If I do that, then there is no way for any class in my
> inheritance hierarchy to own the io_service. As such, I cannot start and
> stop it either.
> 
> Is there any way to get ownership of the io_service in my class hierarchy?

class Server: protected boost::asio::io_service, public Listener
Server (): Listener (*this)

HTH,
Chris