Boost::bind a method with boost::function parameter

Question

I would like to provide an extra boost::function to a async_write. I want the connections own HandleWrite function to be called first and then call the provided boost::function.

Member method of Connection that binds to asio async_write

void Connection::HandleWrite(
    const boost::system::error_code& e,
    boost::function<void (const boost::system::error_code&)> handler)
 {
    // Code removed for clarity

    if(!handler.empty())
        handler(e);
 };

Trying to bind HandleWrite to a asio async_write and provide another bind as the value for handler. This doesn't compile. What am I doing wrong?

  void Connection::QueueRequest(
      boost::shared_array<char> message, 
      std::size_t size, 
      boost::function<void (const boost::system::error_code&)> handler)
  {
     // Code hidden for clarity

     boost::asio::async_write(m_Socket, boost::asio::buffer(buffer),
         boost::bind(&Connection::HandleWrite, shared_from_this(),
            boost::asio::placeholders::error,
            handler
         )
     );
  }

The error message I get from the compiler is the following:

Error 1   error C2825: 'F': must be a class or namespace when followed by '::'    boost\bind\bind.hpp 69
Error   2   error C2039: 'result_type' : is not a member of '`global namespace''    boost\bind\bind.hpp 69
Error   3   error C2146: syntax error : missing ';' before identifier 'type'    boost\bind\bind.hpp 69
Error   4   error C2208: 'boost::_bi::type' : no members defined using this type    boost\bind\bind.hpp 69
Error   5   fatal error C1903: unable to recover from previous error(s); stopping compilation   boost\bind\bind.hpp 69

Answer 1

What error(s) are you getting exactly? I don't see anything obviously wrong in the code shown in your question, so I can't give you a direct answer.

However, Kornel's answer made me doubt, as I thought that the functors generated by boost::bind can take any number of arguments and simply ignore the extra ones.

So I quickly hacked this to verify:

#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/function.hpp>
#include <string>
#include <iostream>


void Foo(const boost::system::error_code&)
{
    // whatever
}

struct Client : boost::enable_shared_from_this<Client>
{
    void HandleWrite(
        const boost::system::error_code& Err, 
        boost::function<void(const boost::system::error_code&)> OtherHandler
    )
    {
        std::cout << "MyHandler(" << Err << ")\n";
        OtherHandler(Err);
    }

    void MakeTheCall(boost::function<void (const boost::system::error_code&)> Other)
    {
        using boost::asio::ip::tcp;

        // Of course, the scope and initialization of
        // io_service, sock and request are all wrong here,
        // as we're only interested in testing if the async_write
        // call below will compile.
        // Don't try to run this at home!
        boost::asio::io_service io_service;
        tcp::socket sock(io_service);
        boost::asio::streambuf request;

        boost::asio::async_write(sock, request,
            boost::bind(&Client::HandleWrite, shared_from_this(),
                boost::asio::placeholders::error,
                Other
            )
        );
    }
};


int main()
{
    boost::shared_ptr<Client> c;
    c->MakeTheCall(boost::bind(&Foo, _1));

    return 0;
}

which is sketching what I guess you're trying to do.

As expected, it does compile, so comparing it with what you're actually doing may help you finding the problem.

Answer 2

The problem turned out to be in another place that used the same HandleWrite function and wasn't bound correctly. After fixing that it compiled.