Question

I’m writing a server with Boost, something pretty simple – accept an XML message, process, reply. But I’m running into trouble at telling it when to stop reading.

This is what I have right now: (_index is the buffer into which the data is read)

std::size_t tcp_connection::completion_condition(const boost::system::error_code& error, 
std::size_t bytes_transferred)
{
    int ret = -1;
    std::istream is(&_index);
    std::string s;
    is >> s;

    if (s.find("</end_tag>") != std::string.npos) ret = 0;
    return ret;
}


void tcp_connection::start()
{
    // Get index from server 
    boost::asio::async_read(_socket, _index, &(tcp_connection::completion_condition), 
        boost::bind(&tcp_connection::handle_read, shared_from_this(), boost::asio::placeholders::error,
      boost::asio::placeholders::bytes_transferred));   
}

This doesn’t compile, since I have to define completion_condition as static to pass it to async_read; and I can’t define _index as static since (obviously) I need it to be specific to the class.

Is there some other way to give parameters to completion_condition? How do I get it to recognize the ending tag and call the reading handler?

Answer 1

You can pass pointers to member functions. The syntax for doing it with C++ is tricky, but boost::bind hides it and makes it fairly easy to do.

An example would be making completion_condition non-static and passing it to async_read as such:boost::bind(&tcp_connection::completion_condition, this, _1, _2)

&tcp_connection::completion_condition is a pointer to the function. this is the object of type tcp_connection to call the function on. _1 and _2 are placeholders; they will be replaced with the two parameters the function is called with.