boost :: asio :: io_service检查是否为空

Question

I am using boost 1.55 ( io_service doc ). I need to call the destructor on my io_service to reset it after power is cycled on my serial device to get new data. The problem is that when the destructor is called twice (re-trying connection), I get a segmentation fault.

In header file

boost::asio::io_service io_service_port_1;

In function that closes connection

io_service_port_1.stop();
io_service_port_1.reset();
io_service_port_1.~io_service();    // how to check for NULL?
                                    // do I need to re-construct it?

The following does not work:

if (io_service_port_1)
if (io_service_port_1 == NULL)

Thank you.

Answer 1

If you need manual control over when the object is created and destroyed, you should be wrapping it in a std::unique_ptr object.

std::unique_ptr<boost::asio::io_service> service_ptr = 
    std::make_unique<boost::asio::io_service>();

/*Do stuff until connection needs to be reset*/
service_ptr->stop();
//I don't know your specific use case, but the call to io_service's member function reset is probably unnecessary.
//service_ptr->reset();
service_ptr.reset();//"reset" is a member function of unique_ptr, will delete object.

/*For your later check*/
if(service_ptr) //returns true if a valid object exists in the pointer
if(!service_ptr) //returns true if no object is being pointed to.

Generally speaking, you should never directly call ~object_name(); . Ever. Ever. Ever. There's several reasons why:

• As a normal part of Stack Unwinding, this will get called anyways when the method returns.
• delete ing a pointer will call it.
• "Smart Pointers" (like std::unique_ptr and std::shared_ptr ) will call it when they self-destruct.

Directly calling ~object_name(); should only ever be done in rare cases, usually involving Allocators, and even then, there are usually cleaner solutions.